£? 

Pr 


IN    COURSE    OF    PUBLICATION. 


Putnam's  Elementary  and  Advanced  Science  Series, 


Adaph 

Printe 

1.  PI 

2.  M 

3AB1 
3BBI 

4.  N. 

5.  PI 

6.  T: 

7.  A: 

8.  A< 

9.  M 

10.  I> 

11.  O 

12.  o: 

13-  M 

14.  A 

15.  Z< 

16.  V 

17.  SI 

19.  M 

20.  N 

21.  N 

22AS' 


GIFT   OF 


'"'isses,  and 

•ents  each. 
By    H. 

By  E. 
>  SLATE 
>RK.  By 
ING  OFF. 
(Camb.,) 
F.R.A.S., 
F.R.A.S., 
es,  A.M., 
11,  Senior 
F.R.A.S., 
,  (Lond.,) 

| 

•all  Poly- 
Science 
'  Schools, 

y  J-   H. 

.  Balfour, 


22BS'- - 

Evers,  LL.D.,  Plymouth. 

23.  PHYSICAL  GEOGRAPHY.     By  John  Macturk,  F.R.G.S. 

24.  PRACTICAL  CHEMISTRY.     By  John  Howard,  London. 

25.  ASTRONOMY.     By  J.  J.  Plummer,  Observatory,  Durham. 


MARINE. 
y    Henry 


7 


IN    COURSE    OF    PUBLICATION. 


ADVANCED   SCIENCE  SERIES. 

% 

Adapted  to  the  requirements  of  Sttidents  in  Science  and  Art  Classes,  and 
Higher  and  Middle  Class  Schools. 

Printed   uniformly  in  I2mo,  averaging  350  pp.,  fully  Illustrated,  cloth 
extra,  price,  $1.25  each. 


1.  PRACTICAL  PLANE  AND  SOLID  GEOMETRY.    By  Professor 

F.  A.  Bradley,  London. 

2.  MACHINE     CONSTRUCTION     AND     DRAWING.     By    E. 

Tomkins,  Queen's  College,  Liverpool. 

3.  BUILDING  CONSTRUCTION.     By  R.  Scott  Burn,  C.E. 

4.  NAVAL  ARCHITECTURE— SHIPBUILDING  AND   LAYING  OFF. 

By  S.  T-  P.  Thearle,  F.R.S.N.A.,  London. 

5.  PURE    MATHEMATICS.     By   Edward   Atkins,   B.Sc.,  (Lond.,) 

Leicester.     2  vols. 

6.  THEORETICAL  MECHANICS.     By  P.  Guthrie  Tail,  Professor 

of  Natural  Philosophy,  Edinburgh. 

7.  APPLIED    MECHANICS.     By    Professor   O.    Reynolds,   Owens 

College,  Manchester. 

8.  ACOUSTICS,   LIGHT  AND   HEAT.     By  W.  S.  Davis,  LL.D., 

Derby. 

9.  MAGNETISM    AND    ELECTRICITY.     By    F.    Guthrie,    B.A., 

Ph.D.,  Royal  School  of  Mines,  London. 

10.  INORGANIC  CHEMISTRY.     By  T.  E.  Thorpe,  Ph.D.,  F.R.S.E., 
Professor     of    Chemistry,     Andersonian      University,     Glasgow. 

2  Vols. 

ir.  ORGANIC  CHEMISTRY.     By  James  Dewar,   F.R.S.E.,  F.C.S., 

Lecturer  on  Chemistry,  Edinburgh. 
12.  GEOLOGY.     By  John  Young,  M.D.,  Professor  of  Natural  History, 

Glasgow  University. 

14.  ANIMAL  PHYSIOLOGY.     By  J.  Cleland,  M.D.,  F.R.S.,  Professor 

of  Anatomy  and  Physiology,  Galway. 

15.  ZOOLOGY.     By  E.  Ray  Lankester,  M.A.,  (Oxon.,)  London.  ft 

16.  VEGETABLE   ANATOMY   AND    PHYSIOLOGY.     By  J.    H. 

Balfour,  M.D.,  Edinburgh  University. 

17.  SYSTEMATIC  AND  ECONOMIC  BOTANY.     By  J.  H.  Balfour, 

M.D.,  Edinburgh  University. 

19.  METALLURGY.     By  W.  H.  Greenwood,  A.R.S.M.     2  Vols. 

20.  NAVIGATION.     By  Henry  Evers,    LL.D.,  Professor   of  Applied 

Mechanics,  Plymouth. 

21.  NAUTICAL  ASTRONOMY.     By  Henry  Evers,  LL.D.,  Plymouth. 

22.  STEAM  AND  THE  STEAM  ENGINE— LAND,  MARINE,  AND 

LOCOMOTIVE.     By  Henry  Evefs,  LL.D.,  Plymouth. 

23.  PHYSICAL  GEOGRAPHY.     By  John  Young,  M.D.,  Professor  of 

Natural  History,  Glasgow  University. 


Map  ) 


The  Sky 
-Km  20,10  PM 
l-Vb  19.  8   PM 
Mur  21 ,  4'. 


Map  III 


The  SUy 
•hil    2Z   10  PM 
Aiu3"o    h   PM 
Se^ft   C.  PM 


PL  ATE  .1. 

ua1i»pie< 

•MapB. 


The  Sky 
Apr  20,10P.M. 
21,8  PAL 
Jun  22,6  P.M. 


The  Sky 
CM  23.10.P.M 
Sov  22.  ft.P.M! 
Dec  21.  G  PM 


lot,' 


Map  [V 


HALF-HOURS 


THE    TELESCOPE; 


BEING    A   POPULAR   GUIDE   TO   THE   USE   OF   THE    TELESCOPE 
AS   A  MEANS   OF   AMUSEMENT   AND   INSTRUCTION. 


KICHAKD    A.    PKOCTOB,    B.A.,   F.R.A.S, 

AUTHOR  OF  "SATURN  AND  ITS  SYSTEM,"  ETC. 


WITH    ILLUSTRATIONS    ON    STONE  AND   WOOD. 


An  undevout  astronomer  is  mad : 

True,  all  things  speak  a  God  ;  but,  in  the  small 

Men  trace  out  Him :  in  great  He  seizes  man. 

YOUNG. 


NEW    YORK: 

G.    P.     PUTNAM'S     SONS. 
1873. 


• 


Main  Lifc* 

. 


LONDON : 

VKINTKD    BY    WILLIAM   CLOWES   AND   SONS,  STAMFOIUJ   STKKET 
AND   CHARING    CROSS. 


PREFACE. 


THE  object  which  the  Author  and  Publisher  of 
this  little  work  have  proposed  to  themselves, 
has  been  the  production,  at  a  moderate  price, 
of  a  useful  and  reliable  guide  to  the  amateur 
telescopist. 

Among  the  celestial  phenomena  described  or 
figured  in  this  treatise,  by  far  the  larger  num 
ber  may  be  profitably  examined  with  small 
telescopes,  and  there  are  none  which  are  beyond 
the  range  of  a  good  3-inch  achromatic. 

The  work  also  treats  of  the  construction  of 
telescopes,  the  nature  and  use  of  star-maps,  and 
other  subjects  connected  with  the  requirements 
of  amateur  observers. 

B.  A.  P. 

January,  1868. 


a  2 

256331 


CONTENTS. 


CHAPTER  I. 

TAGB 
A    HALF-HOUR   ON   THE   STRUCTURE   OF   THE   TELESCOPE      ...         1 


CHAFFER  II. 

A    HALF-HOUR   WITH   ORION,   LEPU8,   TAURUS,   ETC 33 

CHAPTER  III. 

A  HALF-HOUR  WITH  LYRA.  HERCULES,  CORVT'S,  CRATER,   ETC.      47 

CHAPTER  IV. 

A    HALF-HOUR   WITH   BOOTES,   SCORPIO,   OPHIT  CHUS,   ETC.    ...      56 

CHAPTER  V. 

A    HALF-HOUR   WITH   ANDROMEDA,    CYGNUS,   ETC 66 

CHAPTER  VI. 

HALF-HOCRS   WITH   THE   PLANETS  74 

CHAPTER  VII. 

HALF-HOURS   WITH   THE   SUN   AND   MOON       93 


DESCRIPTION   OF   PLATES. 


PLATE  I. — Frontispiece. 

This  plate  presents  the  aspect  of  the  heavens  at  the  four 
seasons,  dealt  with  in  Chapters  II.,  III.,  IV.,  and  V.  In  each 
map  of  this  plate  the  central  point  represents  the  point  verti 
cally  over  the  observer's  head,  and  the  circumference  repre 
sents  his  horizon.  The  plan  of  each  map  is  such  that  the 
direction  of  a  star  or  constellation,  as  respects  the  compass- 
points,  and  its  elevation,  also,  above  the  horizon,  at  the  given 
season,  can  be  at  once  determined.  Two  illustrations  of  the 
use  of  the  maps  will  serve  to  explain  their  nature  better  than 
any  detailed  description.  Suppose  first,  that — at  one  of  the 
hours  named  under  Map  I. — the  observer  wishes  to  find 
Castor  and  Pollux: — Turning  to  Map  I.  he  sees  that  these 
stars  lie  in  the  lower  left-hand  quadrant,  and  very  nearly 
towards  the  point  marked  S.E. ;  that  is,  they  are  to  be  looked 
for  on  the  sky  towards  the  south-east.  Also,  it  is  seen  that 
the  two  stars  lie  about  one-fourth  of  the  way  from  the  centre 
towards  the  circumference.  Hence,  on  the  sky,  the  stars  will 
be  found  about  one-fourth  of  the  way  from  the  zenith  towards 
the  horizon  :  Castor  will  be  seen  immediately  above  Pollux. 
Next,  suppose  that  at  one  of  the  hours  named  the  observer 
wishes  to  learn  what  stars  are  visible  towards  the  west  and 
north-west : — Turning  the  map  until  the  portion  of  the  cir 
cumference  marked  "W N.W.  is  lowermost,  he  sees  that 

in  the  direction  named  the  square  of  Pegasus  lies  not  very 
high  above  the  horizon,  one  diagonal  of  the  square  being 
vertical,  the  other  nearly  horizontal.  Above  the  square  is 


VI  DESCRIPTION    OF    PLATES. 

Andromeda,  to  the  right  of  which  lies  Cassiopeia,  the  stars 
/3  and  e  of  this  constellation  lying  directly  towards  the 
north-west,  while  the  star  o  lies  almost  exactly  midway 
between  the  zenith  and  the  horizon.  Above  Andromeda, 
a  little  towards  the  left,  lies  Perseus,  Algol  being  almost 
exactly  towards  the  west  and  one-third  of  the  way  from  the 
zenith  towards  the  horizon  (because  one-third  of  the  way 
from  the  centre  towards  the  circumference  of  the  map). 
Almost  exactly  in  the  zenith  is  the  star  5  Aurigae. 

The  four  maps  are  miniatures  of  Maps  I.,  IV.,  VII.,  and 
X.  of  my  'Constellation  Seasons,'  fourth-magnitude  stars, 
however,  being  omitted. 


PLATES  II.,  III.,  IV.,  and  V.,  illustrating  Chapters  II.,  III., 
IV.,  and  V. 

Plates  II.  and  IV.  contain  four  star-maps.  They  not  only 
serve  to  indicate  the  configuration  of  certain  important  star- 
groups,  but  they  illustrate  the  construction  of  maps,  such  as 
the  observer  should  make  for  himself  when  he  wishes  to 
obtain  an  accurate  knowledge  of  particular  regions  of  the 
sky.  They  are  all  made  to  one  scale,  and  on  the  conical 
projection — the  simplest  and  best  of  all  projections  for  maps 
of  this  sort.  The  way  in  which  the  meridians  and  parallels 
for  this  projection  are  laid  down  is  described  in  my  '  Hand 
book  of  the  Stars.'  With  a  little  practice  a  few  minutes  will 
suffice  for  sweeping  out  the  equidistant  circular  arcs  which 
mark  the  parallels  and  ruling  in  the  straight  meridians. 

The  dotted  line  across  three  of  the  maps  represents  a 
portion  of  the  horizontal  circle  midway  between  the  zenitb 
and  the  horizon  at  the  hour  at  which  the  map  is  supposed 
to  be  used.  At  other  hours,  of  course,  this  line  would  be 
differently  situated. 

Plates  III.  and  V.  represent  fifty-two  of  the  objects  men 
tioned  in  the  above-named  chapters.  As  reference  is  made  to 
these  figures  in  the  text,  little  comment  is  here  required.  It 
is  to  be  remarked,  however,  that  the  circles,  and  especially 


DESCRIPTION    OF   PLATES.  Vll 

the  small  circles,  do  not  represent  the  whole  of  the  telescope's 
field  of  view,  only  a  small  portion  of  it.  The  object  of  these 
figures  is  to  enable  the  observer  to  know  what  to  expect  when 
he  turns  his  telescope  towards  a  difficult  double  star.  Many 
of  the  objects  depicted  are  very  easy  doubles  :  these  are  given 
as  objects  of  reference.  The  observer  having  seen  the  corres 
pondence  between  an  easy  double  and  its  picture,  as  respects 
the  relation  between  the  line  joining  the  components  and  the 
apparent  path  of  the  double  across  the  telescope's  field  of 
view,  will  know  how  to  interpret  the  picture  of  a  difficult 
double  in  this  respect.  And  as  all  the  small  figures  are 
drawn  to  one  scale,  he  will  also  know  how  far  apart  he  may 
expect  to  find  the  components  of  a  difficult  double.  Thus  he 
will  have  an  exact  conception  of  the  sort  of  duplicity  he  is  to 
look  for,  and  this  is — crede  experto — a  great  step  towards  the 
detection  of  the  star's  duplicity. 


PLATES  VI.  and  VII.,  illustrating  Chapters  VI.  and  VII. 

The  views  of  Mercury,  Venus,  and  Mars  in  these  plates 
(except  the  smaller  view  of  Jupiter  in  Plate  VII.)  are  sup 
posed  to  be  seen  with  the  same  "  power." 

The  observer  must  not  expect  to  see  the  details  presented 
in  the  views  of  Mars  with  anything  like  the  distinctness 
I  have  here  given  to  them.  If  he  place  the  plate  at  a  dis 
tance  of  six  or  seven  yards  he  will  see  the  views  more  nearly 
as  Mars  is  likely  to  appear  in  a  good  three-inch  aperture. 

The  chart  of  Mars  is  a  reduction  of  one  I  have  constructed 
from  views  by  Mr.  Dawes.  I  believe  that  nearly  all  the 
features  included  in  the  chart  are  permanent,  though  not 
always  visible.  I  take  this  opportunity  of  noting  that  the 
eighteen  orthographic  pictures  of  Mars  presented  with  my 
shilling  chart  are  to  be  looked  on  rather  as  maps  than  as 
representing  telescopic  views.  They  illustrate  usefully  the 
varying  presentation  of  Mars  towards  the  earth.  The  observer 
can  obtain  other  such  illustrations  for  himself  by  filling  in 
outlines,  traced  from  those  given  at  the  foot  of  Plate  VI., 


Vlll  DESCRIPTION    OF    PLATES. 

with  details  from  the  chart.  It  is  to  be  noted  that  Mars 
varies  in  presentation,  not  only  as  respects  the  greater  or  less 
opening  out  of  his  equator  towards  the  north  or  south,  but  as 
respects  the  apparent  slope  of  his  polar  axis  to  the  right  or 
left.  The  four  projections  as  shown,  or  inverted,  or  seen  from 
the  back  of  the  plate  (held  up  to  the  light)  give  presentations 
of  Mars  towards  the  sun  at  twelve  periods  of  the  Martial 
year, — viz.,  at  the  autumnal  and  vernal  equinoxes,  at  the 
two  solstices,  and  at  intermediate  periods  corresponding  to 
our  terrestrial  months. 

In  fact,  by  means  of  these  projections  one  might  readily 
form  a  series  of  sun-views  of  Mars  resembling  my  '  Sun-views 
of  the  Earth.' 

In  the  first  view  of  Jupiter  it  is  to  be  remarked  that  the 
three  satellites  outside  the  disc  are  supposed  to  be  moving  in 
directions  appreciably  parallel  to  the  belts  on  the  disc — the 
upper  satellites  from  right  to  left,  the  lower  one  from  left  to 
right.  In  general  the  satellites,  when  so  near  to  the  disc, 
are  not  seen  in  a  straight  line,  as  the  three  shown  in  the 
figure  happen  to  be.  Of  the  three  spots  on  the  disc,  the 
faintest  is  a  satellite,  the  neighbouring  dark  spot  its  shadow, 
the  other  dark  spot  the  shadow  of  the  satellite  close  to  the 
planet's  disc. 


HALF-HOURS  WITH  THE  TELESCOPE. 


CHAPTER  I. 

A  HALF-HOUR  ON  THE  STRUCTURE  OF  THE 
TELESCOPE. 

THERE  are  few  instruments  which  yield  more  plea 
sure  and  instruction  than  the  Telescope.  Even  a 
small  telescope — only  an  inch  and  a  half  or  two 
inches,  perhaps,  in  aperture — will  serve  to  supply 
profitable  amusement  to  those  who  know  how  to 
apply  its  powers.  I  have  often  seen  with  pleasure 
the  surprise  with  which  the  performance  even  of 
an  opera-glass,  well  steadied,  and  directed  towards 
certain  parts  of  the  heavens,  has  been  witnessed 
by  those  who  have  supposed  that  nothing  but  an 
expensive  and  colossal  telescope  could  afford  any 
views  of  interest.  But  a  well-constructed  achro 
matic  of  two  or  three  inches  in  aperture  will  not 
merely  supply  amusement  and  instruction, — it  may 
be  made  to  do  useful  work. 

The  student  of  astronomy  is  often  deterred  from 
telescopic  observation  by  the  thought  that  in  a  field 
wherein  so  many  have  laboured,  with  abilities  and 
means  perhaps  far  surpassing  those  he  may  possess, 
he  is  little  likely  to  reap  results  of  any  utility.  He 
argues  that,  since  the  planets,  stars,  and  nebulae 
have  been  scanned  by  Herschel  and  Kosse,  with 
their  gigantic  mirrors,  and  at  Pulkova  and  Green 
wich  with  refractors  whose  construction  has  taxed 


'2  A   HALF-HOUR    ON    THE 

to  the  utmost  the  ingenuity  of  the  optician  and 
mechanic,  it  must  be  utterly  useless  for  an  unprac 
tised  observer  to  direct  a  telescope  of  moderate 
power  to  the  examination  of  these  objects. 

Now,  passing  over  the  consideration  that  a  small 
telescope  may  afford  its  possessor  much  pleasure 
of  an  intellectual  and  elevated  character,  even  if 
he  is  never  able  by  its  means  to  effect  original 
discoveries,  two  arguments  may  be  urged  in  favour 
of  independent  telescopic  observation.  In  the  first 
place,  the  student  who  wishes  to  appreciate  the 
facts  and  theories  of  astronomy  should  familiarize 
himself  with  the  nature  of  that  instrument  to 
which  astronomers  have  been  most  largely  indebted. 
In  the  second  place,  some  of  the  most  important 
discoveries  in  astronomy  have  been  effected  by 
means  of  telescopes  of  moderate  power  used  skil 
fully  and  systematically.  One  instance  may  suffice 
to  show  what  can  be  done  in  this  way.  The 
well-known  telescopist  Goldschmidt  (who  com 
menced  astronomical  observation  at  the  age  of 
forty-eight,  in  1850)  added  fourteen  asteroids  to 
the  solar  system,  not  to  speak  of  important  dis 
coveries  of  nebulae  and  variable  stars,  by  means  of 
a  telescope  only  five  feet  in  focal  length,  mounted 
on  a  movable  tripod  stand. 

The  feeling  experienced  by  those  who  look 
through  a  telescope  for  the  first  time, — especially 
if  it  is  directed  upon  a  planet  or  nebula — is  com 
monly  one  of  disappointment.  They  have  been 
told  that  such  and  such  powers  will  exhibit  Jupiter's 
belts,  Saturn's  rings,  and  the  continent-outlines  on 
Mars;  yet,  though  perhaps  a  higher  power  is 
applied,  they  fail  to  detect  these  appearances,  and 
can  hardly  believe  that  they  are  perfectly  distinct 
to  the  practised  eye. 

The  expectations  of  the  beginner  are  especially 


STRUCTURE    OF    THE    TELESCOPE.  3 

liable  to  disappointment  in  one  particular.  He 
forms  an  estimate  of  the  view  he  is  to  obtain  of  a 
planet  by  multiplying  the  apparent  diameter  of 
the  planet  by  the  magnifying  power  of  his  telescope, 
and  comparing  the  result  with  the  apparent  diameter 
of  the  sun  or  moon.  Let  us  suppose,  for  instance, 
that  on  the  day  of  observation  Jupiter's  apparent 
diameter  is  45",  and  that  the  telescopic  power  ap 
plied  is  40,  then  in  the  telescope  Jupiter  should 
appear  to  have  a  diameter  of  1800",  or  half  a  degree, 
which  is  about  the  same  as  the  moon's  apparent  dia 
meter.  But  when  the  observer  looks  through  the 
telescope  he  obtains  a  view — interesting,  indeed,  and 
instructive — but  very  different  from  what  the  above 
calculation  would  lead  him  to  expect.  He  sees  a 
disc  apparently  much  smaller  than  the  moon's,  and 
not  nearly  so  well-defined  in  outline ;  in  a  line  with 
the  disc's  centre  there  appear  three  or  four  minute 
dots  of  light,  the  satellites  of  the  planet;  and, 
perhaps,  if  the  weather  is  favourable  and  the 
observer  watchful,  he  will  be  able  to  detect  faint 
traces  of  belts  across  the  planet's  disc. 

Yet  in  such  a  case  the  telescope  is  not  in  fault. 
The  planet  really  appears  of  the  estimated  size. 
In  fact,  it  is  often  possible  to  prove  this  in  a 
very  simple  manner.  If  the  observer  wait  until 
the  planet  and  the  moon  are  pretty  near  together, 
he  will  find  that  it  is  possible  to  view  the  planet 
with  one  eye  through  the  telescope  and  the 
moon  with  the  unaided  eye,  in  such  a  manner  that 
the  two  discs  may  coincide,  and  thus  their  relative 
apparent  dimensions  be  at  once  recognised.  Nor 
should  the  indistinctness  and  incompleteness  of  the 
view  be  attributed  to  imperfection  of  the  telescope ; 
they  are  partly  due  to  the  nature  of  the  observation 
and  the  low  power  employed,  and  partly  to  the 
inexperience  of  the  beginner. 

B  2 


A   HALF-HOUR    ON    THE 

It  is  to  sucli  a  beginner  that  the  following  pages 
are  specially  addressed,  with  the  hope  of  affording 
him  aid  and  encouragement  in  the  use  of  one  of 
the  most  enchanting  of  scientific  instruments, — an 
instrument  that  has  created  for  astronomers  a  new 
sense,  so  to  speak,  by  which,  in  the  words  of  the 
ancient  poet : 

Subjecere  oculis  distantia  sidera  nostris, 
-<Etheraque  ingenio  supposuere  suo. 

In  the  first  place,  it  is  necessary  that  the  begin 
ner  should  rightly  know  what  is  the  nature  of  the 
instrument  he  is  to  use.  And  this  is  the  more 
necessary  because,  while  it  is  perfectly  easy  to 
obtain  such  knowledge  without  any  profound  ac 
quaintance  with  the  science  of  optics,  yet  in  many 
popular  works  on  this  subject  the  really  important 
points  are  omitted,  and  even  in  scientific  works 
such  points  are  too  often  left  to  be  gathered  from  a 
formula.  AYlien  the  observer  has  learnt  what  it  is 
that  his  instrument  is  actually  to  do  for  him,  he 
will  know  how  to  estimate  its  performance,  and 
how  to  vary  the  application  of  its  powers — whether 
illuminating  or  magnifying— according  to  the  nature 
of  the  object  to  be  observed. 

Let  us  consider  what  it  is  that  limits  the  range 
of  natural  vision  applied  to  distant  objects.  What 
causes  an  object  to  become  invisible  as  its  distance 
increases?  Two  things  are  necessary  that  an  object 
should  be  visible.  It  must  be  large  enough  to  be 
appreciated  by  the  eye,  and  it  must  send  light 
enough.  Thus  increase  of  distance  may  render  an 
object  invisible,  either  through  diminution  of  its 
apparent  size,  or  through  diminution  in  the  quan 
tity  of  light  it  sends  to  the  eye,  or  through  both 
these  causes  combined.  A  telescope,  therefore,  or 
(as  its  name  implies)  an  instrument  to  render 


STRUCTURE    OF    THE    TELESCOPE. 


distant  objects  visible,  must  be  both  a  magnifying 
and  an  illuminating  instrument. 

Let  E  F,  fig.  1,  be  an  object,  not  near  to  A  B  as 
in  the  figure,  but  so  far  off  that  the  bounding  lines 
from  A  and  B  would  meet  at  the 
point  corresponding  to  the  point  P. 
Then  if  a  large  convex  glass  A  B 
(called  an  object-glass}  be  interposed 
between  the  object  and  the  eye,  all 
those  rays  which,  proceeding  from 
P,  fall  on  A  B,  will  be  caused  to 
converge  nearly  to  a  point  p.  The 
same  is  true  for  every  point  of  the 
object  E  M  F,  and  thus  a  small 
image,  e  m  f,  will  be  formed.  This 
image  will  not  lie  exactly  on  a  flat 
surface,  but  will  be  curved  about 
the  point  midway  between  A  and 
B  as  a  centre.  Now  if  the  lens 
A  B  is  removed,  and  an  eye  is 
placed  at  m  to  view  the  distant  ob 
ject  E  M  F,  those  rays  only  from  I 
each  point  of  the  object  which 
fall  on  the  pupil  of  the  eye  (whose 
diameter  is  about  equal  to  m  p  sup 
pose)  will  serve  to  render  the  ob 
ject  visible.  On  the  other  hand, 
every  point  of  the  image  e  rn  f  has 
received  the  whole  of  the  light 
gathered  up  by  the  large  glass  A  B. 

If   then    we    can    only  make    this  ^ H 

light  available.,  it  is  clear  that  we" 
shall    have    acquired    a    large   in-  ^'9.  1. 

crease  of  light  from  the  distant  object.  Now  it  will 
be  noticed  that  the  light  which  has  converged  to 
p^  diverges  from  p  so  that  an  eye,  placed  that 
this  diverging  pencil  of  rays  may  fall  upon  it, 


0  A    HALF-HOUR    ON    THE 

would  be  too  small  to  receive  the  whole  of 
the  pencil.  Or,  if  it  did  receive  the  whole  of  this 
pencil,  it  clearly  could  not  receive  the  whole  of 
the  pencils  proceeding  from  other  parts  of  the 
image  e  m  f.  Something  would  be  gained,  though, 
even  in  this  case,  since  it  is  clear  that  an  eye  thus 
placed  at  a  distance  of  ten  inches  from  e  m  f  (which 
is  about  the  average  distance  of  distinct  vision) 
would  not  only  receive  much  more  light  from  the 
image  e  m  /,  than  it  would  from  the  object  E  M  F, 
but  see  the  image  much  larger  than  the  object.  It 
is  in  this  way  that  a  simple  object-glass  forms  a 
telescope,  a  circumstance  we  shall  presently  have  to 
notice  more  at  length.  But  we  want  to  gain  the 
full  benefit  of  the  light  which  has  been  gathered  up 
for  us  by  our  object-glass.  We  therefore  interpose 
a  small  convex  glass  a  b  (called  an  eye-glass)  be 
tween  the  image  and  the  eye,  at  such  a  distance 
from  the  image  that  the  divergent  pencil  of  rays 
is  converted  into  a  pencil  of  parallel  or  nearly 
parallel  rays.  Call  this  an  emergent  pencil.  Then 
all  the  emergent  pencils  now  converge  to  a  point 
on  the  axial  line  m  M  (produced  beyond  m),  and  an 
eye  suitably  placed  can  take  in  all  of  them  at  once, 
Thus  the  whole,  or  a  large  part,  of  the  image  is  seen 
at  once.  But  the  image  is  seen  inverted  as  shown. 
This  is  the  Telescope,  as  it  was  first  discovered, 
and  such  an  arrangement  would  now  be  called  a 
simple  astronomical  Telescope. 

Let  us  clearly  understand  what  each  part  of  the 
astronomical  telescope  does  for  us  : — 

The  object-glass  A  B  gives  us  an  illuminated 
image,  the  amount  of  illumination  depending  on 
the  size  of  the  object-glass.  The  eye-glass  enables 
us  to  examine  the  image  microscopically. 

We  may  apply  eye-glasses  of  different  focal 
length.  It  is  clear  that  the  shorter  the  focal  length 


STRUCTURE    OF    THE    TELESCOPE.  7 

of  a  6,  the  nearer  must  a  b  be  placed  to  the  image, 
and  the  smaller  will  the  emergent  pencils  be,  but 
the  greater  the  magnifying  power  of  the  eye-glass. 
If  the  emergent  pencils  are  severally  larger  than 
the  pupil  of  the  eye,  light  is 
wasted  at  the  expense  of  mag 
nifying  power.  Therefore  the 
eye-glass  should  never  be  of 
greater  focal  length  than  that 
which  makes  the  emergent  pen 
cils  about  equal  in  diameter  to 
the  pupil  of  the  eye.  On  the 
other  hand,  the  eye-glass  must 
not  be  of  such  small  focal  length 
that  the  image  appears  indistinct 
and  contorted,  or  dull  for  want  of 
light. 

Let  us  compare  with  the  ar 
rangement  exhibited  in  fig.  1  that 
adopted  by  Galileo.  Surprise  is 
sometimes  expressed  that  this  in 
strument,  which  in  the  hands  of 
the  great  Florentine  astronomer 
effected  so  much,  should  now  be 
known  as  the  non-  astronomical 
Telescope.  I  think  this  will  be 
readily  understood  when  we  com 
pare  the  two  arrangements. 

In   the    Galilean   Telescope    a 

small  concave  eye-glass,  a  b  (fig.     ^ ^ ^^ 

2),  is  placed  between  the  object- 
glass  and  the  image.     In  fact,  no  Fi$-  2- 
image  is   allowed  to   be   formed 
in  this   arrangement,   but    the  convergent   pencils 
are  intercepted  by  the  concave  eye-glass,  and  con 
verted  into  parallel  emergent  pencils.    Now  in  fig.  2 
the  concave  eye-glass   is   so   placed  as  to  receive 


A    HALF-HOUil    ON    THE 

only  ^  a  part  of  the  convergent  pencil  A  p  B,  and 
this  is  the  arrangement  usually  adopted.  By  using 
a  concave  glass  of  shorter  focus,  which  would  there 
fore  be  placed  nearer  to  m  p,  the  whole  of  the  con 
vergent  pencil  might  be  received  in  this  as  in  the 
former  case.  But  then  the  axis  of  the  emergent 
pencil,  instead  of  returning  (as  we  see  it  in  fig.  1) 
towards  the  axis  of  the  telescope,  would  depart  as 
much  from  that  axis.  Thus  there  would  be  no  point 
on  the  axis  at  which  the  eye  could  be  so  placed  as 
to  receive  emergent  pencils  showing  any  considerable 
part  of  the  object.  The  difference  may  be  compared 
to  that  between  looking  through  the  small  end  of  a 
cone-shaped  roll  of  paper  and  looking  through  the 
large  end ;  in  the  former  case  the  eye  sees  at  once  all 
that  is  to  be  seen  through  the  roll  (supposed  fixed 
in  position),  in  the  latter  the  eye  may  be  moved 
about  so  as  to  command  the  same  range  of  view, 
but  at  any  instant  sees  over  a  much  smaller  range. 

To  return  to  the  arrangement  actually  employed, 
which  is  illustrated  by  the  common  opera-glass.  We 
see  that  the  full  illuminating  power  of  the  telescope 
is  not  brought  into  play.  But  this  is  not  the  only 
objection  to  the  Galilean  Telescope.  It  is  obvious 
that  if  the  part  C  D  of  the  object-glass  were  covered, 
the  point  P  would  not  be  visible,  whereas,  in  the 
astronomical  arrangement  no  other  effect  is  produced 
on  the  visibility  of  an  object,  by  covering  part  of  the 
object-glass,  than  a  small  loss  of  illumination.  In 
other  words,  the  dimensions  of  the  field  of  view  of 
a  Galilean  Telescope  depend  on  the  size  of  the 
object-glass,  whereas  in  the  astronomical  Telescope 
the  field  of  view  is  independent  of  the  size  of  the 
object-glass.  The  difference  may  be  readily  tested. 
If  we  direct  an  opera-glass  upon  any  object,  we 
shall  find  that  any  covering  placed  over  a  part  of 
the  object-glass  becomes  visible  when  we  look  through 


STRUCTURE    OF    THE    TELESCOPE. 

tlie  instrument,  interfering  therefore  pro  tantowiila.  the 
range  of  view.  A  covering  similarly  placed  on  any 
part  of  the  object-glass  of  an  astronomical  telescope 
does  not  become  visible  when  we  look  through  the 
instrument.  The  distinction  has  a  very  important 
bearing  011  the  theory  of  telescopic  vision. 

In  considering  the  application  of  the  telescope 
to  practical  observation,  the  circumstance  that  in 
the  Galilean  Telescope  no  real  image  is  formed,  is 
yet  more  important.  A  real  image  admits  of  mea 
surement,  linear  or  angular,  while  to  a  virtual  image 
(such  an  image,  for  instance,  as  is  formed  by  a 
common  looking-glass)  no  such  process  can  be  ap 
plied.  In  simple  observation  the  only  noticeable 
effect  of  this  difference  is  that,  whereas  in  the 
astronomical  Telescope  a  stop  or  diaphragm  can  be 
inserted  in  the  tube  so  as  to  cut  off  what  is  called 
the  ragged  edge  of  the  field  of  view  (which  includes 
all  the  part  not  reached  by  full  pencils  of  light  from 
the  object-glass),  there  is  no  means  of  remedying  the 
corresponding  defect  in  the  Galilean  Telescope.  It 
would  be  a  very  annoying  defect  in  a  telescope 
intended  for  astronomical  observation,  since  in 
general  the  edge  of  the  field  of  view  is  not  percep 
tible  at  night.  The  unpleasant  nature  of  the  defect 
may  be  seen  by  looking  through  an  opera-glass,  and 
noticing  the  gradual  fading  away  of  light  round  the 
circumference  of  the  field  of  view. 

The  properties  of  reflection  as  well  as  of  refrac 
tion  have  been  enlisted  into  the  service  of  the  astro 
nomical  observer.  The  formation  of  an  image  by 
means  of  a  concave  mirror  is  exhibited  in  fig.  3.  As 
the  observer's  head  would  be  placed  between  the 
object  and  the  mirror,  if  the  image,  formed  as  in 
fig.  3,  were  to  be  microscopically  examined,  various 
devices  are  employed  .in  the  construction  of  reflect 
ing  telescopes  to  avoid  the  loss  of  light  which  would 


10 


A    HALF-HOUR    ON    THE 


s<~~T~n 


result — a  loss  which  would  be  important  even  with 
the  largest  mirrors  yet  constructed.     Thus,  in  Gre 
gory's  Telescope,  a  small  mirror,  having  its  con 
cavity  towards  the  great  one,  is  placed  in  the  axis 
of  the  tube  and   forms  an  image 
•«*» S£ ^--    which  is  viewed  through  an  aper 
ture  in   the   middle  of  the  great 
mirror.     A  similar  plan  is  adopted 
in  Cassegrain's  Telescope,  a  small 
convex  mirror  replacing  the  con 
cave  one.     In  Newton's  Telescope 
a  small  inclined-plane  reflector  is 
used,   which   sends   the  pencil  of 
light    off    at    right-angles    to    the 
axis  of  the   tube.     In  Herschel's 
Telescope  the  great  mirror  is  in 
clined  so  that  the  image  is  formed 
at  a  slight  distance  from  the  axis 
of  the  telescope.     In  the  two  first 
cases  the  object  is  viewed  in  the 
usual   or   direct    way,    the   image 
being  erect  in  Gregory's  and  in 
verted    in    Cassegrain's.      In    the 
third   the  observer  looks  through 
the   side  of  the   telescope,  seeing 
an   inverted  image  of  the   object, 
In  the  last  the  observer  sees  the 
object  inverted,  but  not  altered  as 
respects  right  and  left.     The  last- 
mentioned  method  of  viewing  ob 
jects  is  the  only  one  in  which  the 
observer's  back  is  turned  towards 
the  object,  yet  this  method  is  called 
the  front  view — apparently  quasi  lucus  a  non  lucendo. 
It  appears,  then,  that  in  all  astronomical  Tele 
scopes,  reflecting  or  refracting,  a  real  image  of  an 
object  is   submitted  to  microscopical    examination. 


L_U 


Fig. 


STRUCTURE    OF    THE    TELESCOPE.  11 

Of  this  fact  the  possessor  of  a  telescope  may  easily 
assure  himself;  for  if  the  eye-glass  be  removed,  and 
a  small  screen  be  placed  at  the  focus  of  the  object- 
glass,  there  will  appear  upon  the  screen  a  small  pic 
ture  of  any  object  towards  which  the  tube  is  turned. 
But  the  image  may  be  viewed  in  another  way  which 
requires  to  be  noticed.  If  the  eye,  placed  at  a  dis 
tance  of  five  or  six  inches  from  the  image,  be  directed 
down  the  tube,  the  image  will  be  seen  as  before ;  in 
fact,  just  as  a  single  convex  lens  of  short  focus  is  the 
simplest  microscope,  so  a  simple  convex  lens  of  long 
focus  is  the  simplest  telescope.*  But  a  singular 
circumstance  will  immediately  attract  the  observer's 
notice.  A  real  picture,  or  the  image  formed  on  the 
screen  as  in  the  former  case,  can  be  viewed  at  varying 
distances ;  but  when  we  view  the  image  directly,  it 
will  be  found  that  for  distinct  vision  the  eye  must 
be  placed  almost  exactly  at  a  fixed  distance  from  the 
image.  This  peculiarity  is  more  important  than  it 
might  be  thought  at  first  sight.  In  fact,  it  is  essen 
tial  that  the  observer  who  would  rightly  apply  the 
powers  of  his  telescope,  or  fairly  test  its  perform 
ance,  should  understand  in  what  respect  an  image 
formed  by  an  object-glass  or  object-mirror  differs 
from  a  real  object. 

The  peculiarities  to  be  noted  are  the  curvature, 
indistinctness,  and  false  colouring  of  the  image. 

The  curvature  of  the  image  is  the  least  important 
of  the  three  defects  named — a  fortunate  circum- 
*  Such  a  telescope  is  most  powerful  with  the  shortest 
sight.  It  may  be  remarked  that  the  use  of  a  telescope  often 
reveals  a  difference  in  the  sight  of  the  two  eyes.  In  my  own 
case,  for  instance,  I  have  found  that  the  left  eye  is  very 
short-sighted,  the  sight  of  the  right  eye  being  of  about  the 
average  range.  Accordingly  with  my  left  eye  a  5^-foot 
object-glass,  alone,  forms  an  effective  telescope,  with  which 
I  can  see  Jupiter's  moons  quite  distinctly,  and  under  favour 
able  circumstances  even  Saturn's  rings.  I  find  that  the  full 
moon  is  too  bright  to  be  observed  in  this  way  without  pain, 
except  at  low  altitudes. 


12  A    HALF-HOUR    ON   THE 

stance,  since  this  defect  admits  neither  of  remedy 
nor  modification.  The  image  of  a  distant  object, 
instead  of  lying  in  a  plane,  that  is,  forming  what  is 
technically  called  a  flat  field,  forms  part  of  a  spheri 
cal  surface  whose  centre  is  at  the  centre  of  the  object- 
glass.  Hence  the  centre  of  the  field  of  view  is 
somewhat  nearer  to  the  eye  than  are  the  outer  parts 
of  the  field.  The  amount  of  curvature  clearly  de 
pends  on  the  extent  of  the  field  of  view,  and  there 
fore  is  not  great  in  powerful  telescopes.  Thus,  if 
we  suppose  that  the  angular  extent  of  the  field  is 
about  half  a  degree  (a  large  or  low-power  field),  the ' 
centre  is  nearer  than  the  boundary  of  the  field  by 
about  1-3 2 Oth  part  only  of  the  field's  diameter. 

The  indistinctness  of  the  image  is  partly  due  to 
the  obliquity  of  the  pencils  which  form  parts  of  the 
image,  and  partly  to  what  is  termed  spherical  aber 
ration.  The  first  cause  cannot  be  modified  by  the 
optician's  skill,  and  is  not  important  when  the  field 
of  view  is  small.  Spherical  aberration  causes  those 
parts  of  a  pencil  which  fall  near  the  boundary  of  a 
convex  lens  to  converge  to  a  nearer  (i.  e.  shorter) 
focus  than  those  which  fall  near  the  centre.  This 
may  be  corrected  by  a  proper  selection  of  the  forms 
of  the  two  lenses  which  replace,  in  all  modern 
telescopes,  the  single  lens  hitherto  considered. 

The  false  colouring  of  the  image  is  due  to  chro 
matic  aberration.  The  pencil  of  light  proceeding 
from  a  point,  converges,  not  to  one  point,  but  to 
a  short  line  of  varying  colour.  Thus  a  series  of 
coloured  images  is  formed,  at  different  distances 
from  the  object-glass.  So  that,  if  a  screen  were 
placed  to  receive  the  mean  image  in  focus,  a  coloured 
fringe  due  to  the  other  images  (ont  of  focus,  and 
therefore  too  large)  would  surround  the  mean  image. 

Newton  supposed  that  it  was  impossible  to  get 
rid  of  this  defect,  and  therefore  turned  his  attention 
to  the  construction  of  reflectors.  But  the  discovery 


STRUCTURE    OF    THE    TELESCOPE. 


13 


that  the  dispersive  powers  of  different  glasses  are 
not  proportional  to  their  reflective  powers,  supplied 
opticians  with  the  means  of  remedying  the  defect. 
Let  us  clearly  understand  what  is  the  discovery 
referred  to.  If  with  a  glass  prism  of  a  certain  form 
we  produce  a  spectrum  of  the  sun,  this  spectrum 
will  be  thrown  a  certain  distance  away  from  the 
point  on  which  the  sun's  rays  would  fall  if  not 
interfered  with.  This  distance  depends  on  the  re 
fractive  power  of  the  glass.  The  spectrum  will 
have  a  certain  length,  depending  on  the  dispersive 
power  of  the  glass.  Now,  if  we  change  our  prism 
for  another  of  exactly  the  same  shape,  'but  made  of 
a  different  kind  of  glass,  we  shall  find  the  spectrum 
thrown  to  a  different  spot.  If  it  appeared  that  the 
length  of  the  new  spectrum  was  increased  or  dimi 
nished  in  exactly  the  same  proportion  as  its  distance 
from  the  line  of  the  sun's  direct  light,  it  would  have 
been  hopeless  to  attempt  to  remedy  chromatic  aber 
ration.  Newton  took  it  for  granted  that  this  was 
so.  But  the  experiments  of  Hall  and  the  Dollonds 
showed  that  there  is  no  such  strict  pro 
portionality  between  the  dispersive  and 
refractive  powers  of  different  kinds  of 
glass.  It  accordingly  becomes  possible 
to  correct  the  chromatic  aberration  of 
one  glass  by  superadding  that  of  another. 

This  is  effected  by  combining,  as 
shown  in  fig.  4,  a  convex  lens  of  crown 
glass  with  a  concave  lens  of  flint  glass, 
the  '  convex  lens  being  placed  nearest 
to  the  object.  A  little  colour  still 
remains,  but  not  enough  to  interfere 
seriously  with  the  distinctness  of  the 
image. 

But  even  if  the  image  formed  by  the 
object-glass  were  perfect,  yet  this  image,  viewed 


Fig.  4. 


14  A    HALF-HOUR   ON   THE 

through  a  single  convex  lens  of  short  foe  as  placed  as 
in  fig.  1,  would  appear  curved,  indistinct,  coloured, 
and  also  distorted,  because 
viewed  by  pencils  of  light 
which  do  not  pass  through 
the  centre  of  the  eye-glass. 
These  effects  can  be  dimi- 
nished  (but  not  entirely  re 
moved  together •)  by  using  an 
eye-piece  consisting  of  two  lenses  instead  of  a  single 
eye-glass.  The  two  forms  of  eye-piece  most  com 
monly  employed  are  exhibited  in  figs.  5  and  6.  Fig. 
5  is  Huyghens'  eye-piece,  called  also  the  negative  eye 
piece,  because  a  real  image 
is  formed  behind  the  field- 
glass  (the  lens  which  lies 
nearest  to  the  object-glass). 
Fig.  6  represents  Rams- 
den's  eye-piece,  called  also 
Fig.  6.  the  positive  eye-piece,  be 

cause  the  real  image  formed 
by  the  object-glass  lies  in  front  of  the  field-glass. 

The  course  of  a  slightly  oblique  pencil  through 
either  eye-piece  is  exhibited  in  the  figures.  The 
lenses  are  usually  plano-convex,  the  convexities 
being  turned  towards  the  object-glass  in  the  nega 
tive  eye-piece,  and  towards  each  other  in  the  positive 
eye-piece.  Coddington  has  shown,  however,  that 
the  best  forms  for  the  lenses  of  the  negative  eye 
piece  are  those  shown  in  fig.  5. 

The  negative  eye-piece,  being  achromatic,  is  com 
monly  employed  in  all  observations  requiring  dis 
tinct  vision  only.  But  as  it  is  clearly  unfit  for 
observations  requiring  inicrometrical  measurement, 
or  reference  to  fixed  lines  at  the  focus  of  the 
object-glass,  the  positive  eye-piece  is  used  for  these 
purposes. 


STRUCTURE    OF    THE    TELESCOPE.  15 

For  observing  objects  at  great  elevations  the 
diagonal  eye-tube  is  often  convenient.  Its  con 
struction  is  shown  in  fig.  7.  A  B  C  is  a  totally 
reflecting  prism  of  glass. 
The  rays  from  the  object- 
glass  fall  on  the  face  A  B, 
are  totally  reflected  on 
the  face  B  C,  and  emerge 
through  the  face  A  C. 
In  using  this  eye-piece, 
it  must  be  remembered 
that  it  lengthens  the 
sliding  eye-tube,  which 
must  therefore  be  thrust 
further  in,  or  the  object 
will  not  be  seen  in  focus. 
There  is  an  arrangement  by  which  the  change  of 
direction  is  made  to  take  place  between  the  two 
glasses  of  the  eye-piece.  With  this  arrangement 
(known  as  the  diagonal  eye-piece)  no  adjustment  of 
the  eye-tube  is  required.  However,  for  amateurs' 
telescopes  the  more  convenient  arrangement  is  the 
diagonal  eye-tube,  since  it  enables  the  observer  to 
apply  any  eye-piece  he  chooses,  just  as  with  the 
simple  sliding  eye-tube. 

We  come  next  to  the  important  question  of  the 
mounting  of  our  telescope. 

The  best  known,  and,  in  some  respects,  the  sim 
plest  method  of  mounting  a  telescope  for  general 
observation  is  that  known  as  the  altitude-and-azimuth 
mounting.  In  this  method  the  telescope  is  pointed 
towards  an  object  by  two  motions, — one  giving  the 
tube  the  required  altitude  (or  elevation),  the  other 
giving  it  the  required  azimuth  (or  direction  as  respects 
the  compass  points) . 

For  small  alt-azimuths  the  ordinary  pillar-and- 
claw  stand  is  sufficiently  steady.  For  larger  instru- 


16  A    HALF-HOUK   ON    THE 

ments  other  arrangements  are  needed,  both  to  give 
the  telescope  steadiness,  and  to  supply  slow  move 
ments  in  altitude  and  azimuth.  The  student  will 
find  no  difficulty  in  understanding  the  arrangement 
of  sliding-tubes  and  rack-work  commonly  adopted. 
This  arrangement  seems  to  me  to  be  in  many 
respects  defective,  however.  The  slow  movement 
in  altitude  is  not  uniform,  but  varies  in  effect  ac 
cording  to  the  elevation  of  the  object  observed.  It 
is  also  limited  in  range;  and  quite  a  little  series 
of  operations  has  to  be  gone  through  when  it  is 
required  to  direct  the  telescope  towards  a  new 
quarter  of  the  heavens.  However  expert  the  ob 
server  may  become  by  practice  in  effecting  these 
operations,  they  necessarily  take  up  some  time  (per 
formed  as  they  must  be  in  the  dark,  or  by  the  light 
of  a  small  lantern),  and  during  this  time  it  often 
happens  that  a  favourable  opportunity  for  observa 
tion  is  lost. 

These  disadvantages  are  obviated  when  the  tele 
scope  is  mounted  in  such  a  manner  as  is  exhibited 
in  fig.  8,  which  represents  a  telescope  of  my  own 
construction.  The  slow  movement  in  altitude  is 
given  by  rotating  the  rod  h  e,  the  endless  screw  in 
which  turns  the  small  wheel  at  b,  whose  axle  in 
turn  bears  a  pinion-wheel  working  in  the  teeth  of 
the  quadrant  a.  The  slow  movement  in  azimuth  is 
given  in  like  manner  by  rotating  the  rod  h'  e',  the 
lantern- wheel  at  the  end  of  "Vhich  turns  a  crown 
wheel  on  whose  axle  is  a  pinion-wheel  working  in 
the  teeth  of  the  circle  c.  The  casings  at  e  and  e', 
in  which  the  rods  he  and  h' e'  respectively  work, 
are  so  fastened  by  elastic  cords  that  an  upward 
pressure  on  the  handle  /*,  or  a  downward  pressure 
on  the  handle  h',  at  once  releases  the  endless  screw 
or  the  crown-wheel  respectively,  so  that  the  tele 
scope  can  be  swept  at  once  through  any  desired 


STRUCTURE    OP    THE    TELESCOPE. 


17 


Fig.  8. 

angle  in  altitude  or  azimuth.  This  method  of 
mounting  has  other  advantages;  the  handles  are 
conveniently  situated  and  constant  in  position ;  also, 
as  they  do  not  work  directly  on  the  telescope, 


18  A   HALF-HOUR    ON    THE 

they  can  be  turned  without  setting  the  tube  in 
vibration. 

I  do  not  recommend  the  mounting  to  be  exactly 
as  shown  in  fig.  8.  That  method  is  much  too  ex 
pensive  for  an  alt-azimuth.  But  a  simple  arrange 
ment  of  belted  wheels  in  place  of  the  toothed  wheels 
a  and  c  might  very  readily  be  prepared  by  the  inge 
nious  amateur  telescopist;  and  I  feel  certain  that 
the  comfort  and  convenience  of  the  arrangement 
would  amply  repay  him  for  the  labour  it  would  cost 
him.  My  own  telescope— though  the  large  toothed- 
wheel  and  the  quadrant  were  made  inconveniently 
heavy  (through  a  mistake  of  the  workman  who  con 
structed  the  instrument) — worked  as  easily  and 
almost  as  conveniently  as  an  equatorial. 

Still,  it  is  well  for  the  observer  who  wishes  sys 
tematically  to  survey  the  heavens — and  who  can 
afford  the  expense — to  obtain  a  well-mounted  equa 
torial.  In  this  method  of  mounting,  the  main  axis 
is  directed  to  the  pole  of  the  heavens ;  the  other 
axis,  at  right  angles  to  the  first,  carries  the  tele 
scope-tube.  One  of  the  many  methods  adopted  for 
mounting  equatorials  is  that  exhibited — with  the 
omission  of  some  minor  details — in  fig.  9.  a  is  the 
polar  axis,  b  is  the  axis  (called  the  declination  axis) 
which  bears  the  telescope.  The  circles  c  and  d 
serve  to  indicate,  by  means  of  verniers  revolving 
with  the  axes,  the  motion  of  the  telescope  in  right 
ascension  and  declination,  respectively.  The  weight 
w  serves  to  counterpoise  the  telescope,  and  the 
screws  s,  s,  s,  s,  serve  to  adjust  the  instrument  so 
that  the  polar  axis  shall  be  in  its  proper  position. 
The  advantage  gained  by  the  equatorial  method  of 
mounting  is  that  only  one  motion  is  required  to 
follow  a  star.  Owing  to  the  diurnal  rotation  of  the 
earth,  the  stars  appear  to  move  uniformly  in  circles 
parallel  to  the  celestial  equator ;  and  it  is  clear  that 


STRUCTURE    OF    THE    TELESCOPE. 


19 


Fig.  9. 

a  star  so  moving  will  be  kept  in  the  field  of  view, 
the  telescope,  once  directed  to  the  star,  be  made 

to  revolve  uniformly  and  at  a  proper  rate  round  the 

polar  axis. 

The  equatorial  can  be  directed  by  means  of  the 

c  2 


20  A    HALF-HOUR    ON    THE 

circles  c  and  d  to  any  celestial  object  whose  right 
ascension  and  declination  are  known.  On  the  other 
hand,  to  bring  an  object  into  the  field  of  view  of  an 
alt-azimuth,  it  is  necessary,  either  that  the  object 
itself  should  be  visible  to  the  naked  eye,  or  else 
that  the  position  of  the  object  should  be  pretty 
accurately  learned  from  star-maps,  so  that  it  may  be 
picked  up  by  the  alt-azimuth  after  a  little  searching. 
A  small  telescope  called  &  finder  is  usually  attached 
to  all  powerful  telescopes  intended  for  general  ob 
servation.  The  finder  has  a  large  field  of  view, 
and  is  adjusted  so  as  to  have  its  axis  parallel  to 
that  of  the  large  telescope.  Thus  a  star  brought 
to  the  centre  of  the  large  field  of  the  finder  (indi 
cated  by  the  intersection  of  two  lines  placed  at  the 
focus  of  the  eye-glass)  is  at,  or  very  near,  the  centre 
of  the  small  field  of  the  large  telescope. 

If  a  telescope  has  no  finder,  it  will  be  easy  for 
the  student  to  construct  one  for  himself,  and  will 
be  a  useful  exercise  in  optics.  Two  convex  lenses 
not  very  different  in  size  from  those  shown  in  fig.  1, 
and  placed  as  there  shown — the  distance  between 
them  being  the  sum  of  the  focal  lengths  of  the  two 
glasses — in  a  small  tube  of  card,  wood,  or  tin,  will 
serve  the  purpose  of  a  finder  for  a  small  telescope. 
It  can  be  attached  by  wires  to  the  telescope-tube, 
and  adjusted  each  night  before  commencing  observa 
tion.  The  adjustment  is  thus  managed: — a  low 
power  being  applied  to  the  telescope,  the  tube  is 
turned  towards  a  bright  star ;  this  is  easily  effected 
with  a  low  power ;  then  the  finder  is  to  be  fixed,  by 
means  of  its  wires,  in  such  a  position  that  the  star 
shall  be  in  the  centre  of  the  field  of  the  finder  when 
also  in  the  centre  of  the  telescope's  field.  When 
this  has  been  done,  the  finder  will  greatly  help  the 
observations  of  the  evening ;  since  with  high  powers 
much  time  would  be  wasted  in  bringing  an  object 


STRUCTURE    OF    THE    TELESCOPE.  21 

into  the  field  of  view  of  the  telescope  without  the 
aid  of  a  finder.  Yet  more  time  would  be  wasted  in 
the  case  of  an  object  not  visible  to  the  naked  eye, 
but  whose  position  with  reference  to  several  visible 
stars  is  known ;  since,  while  it  is  easy  to  bring  the 
point  required  to  the  centre  of  the  finder's  field,  in 
which  the  guiding  stars  are  visible,  it  is  very  diffi 
cult  to  direct  the  telescope's  tube  on  a  point  of  this 
sort.  A  card  tube  with  wire  fastenings,  such  as 
we  have  described,  may  appear  a  very  insignificant 
contrivance  to  the  regular  observer,  with  his  well- 
mounted  equatorial  and  carefully-adjusted  finder. 
But  to  the  first  attempts  of  the  amateur  observer  it 
affords  no  insignificant  assistance,  as  I  can  aver 
from  my  own  experience.  Without  it — a  superior 
finder  being  wanting — our  "  half-hours  "  would  soon 
be  wasted  away  in  that  most  wearisome  and  annoying 
of  all  employments,  trying  to  "  pick  up  "  celestial 
objects. 

It  behoves  me  at  this  point  to  speak  of  star-maps. 
Such  maps  are  of  many  different  kinds.  There  are 
the  Observatory  maps,  in  which  the  places  of  thou 
sands  of  stars  are  recorded  with  an  amazing  accu 
racy.  Our  beginner  is  not  likely  to  make  use  of,  or 
to  want,  such  maps  as  these.  Then  there  are  maps 
merely  intended  to  give  a  good  general  idea  of  the 
appearance  of  the  heavens  at  different  hours  and 
seasons.  Plate  I.  presents  four  maps  of  this  sort ; 
but  a  more  complete  series  of  eight  maps  has  been 
published  by  Messrs.  Walton  and  Maberly  in  an 
octavo  work ;  and  my  own  '  Constellation-Seasons  ' 
give,  at  the  same  price,  twelve  quarto  maps  (of  four 
of  which  those  in  Plate  I.  are  miniatures),  showing 
the  appearance  of  the  sky  at  any  hour  from  month 
to  month,  or  on  any  night,  at  successive  intervals  of 
two  hours.  But  maps  intermediate  in  character  to 
these  and  to  Observatory  maps  are  required  by  the 


22  A   HALF-HOUR    ON    THE 

amateur  observer.  Such  are  the  Society's  six  gno- 
monic  maps,  the  set  of  six  gnomonic  maps  in  John- 
stone's  '  Atlas  of  Astronomy,'  and  my  own  set  of 
twelve  gnomonic  maps.  The  Society's  maps  are  a 
remarkably  good  set,  containing  on  the  scale  of 
a  ten-inch  globe  all  the  stars  in  the  Catalogue  of  the 
Astronomical  Society  (down  to  the  fifth  magnitude). 
The  distortion,  however,  is  necessarily  enormous 
when  the  celestial  sphere  is  presented  in  only  six 
gnomonic  maps.  In  my  maps  all  the  stars  of  the 
British  Association  Catalogue  down  to  the  fifth 
magnitude  are  included  on  the  scale  of  a  six-inch 
globe.  The  distortion  is  scarcely  a  fourth  of  that 
in  the  Society's  maps.  The  maps  are  so  arranged 
that  the  relative  positions  of  all  the  stars  in  each 
hemisphere  Can  be  readily  gathered  from  a  single 
view ;  and  black  duplicate-maps  serve  to  show  the 
appearance  of  the  constellations. 

It  is  often  convenient  to  make  small  maps  of 
a  part  of  the  heavens  we  may  wish  to  study  closely. 
My  '  Handbook  of  the  Stars '  has  been  prepared  to 
aid  the  student  in  the  construction  of  such  maps. 

In  selecting  maps  it  is  well  to  be  able  to  recog 
nise  the  amount  of  distortion  and  scale-variation. 
This  may  be  done  by  examining  the  spaces  included 
between  successive  parallels  and  meridians,  near  the 
edges  and  angles  of  the  maps,  and  comparing  these 
either  with  those  in  the  centre  of  the  map,  or  with 
the  known  figures  and  dimensions  of  the  corre 
sponding  spaces  on  a  globe. 

We  may  now  proceed  to  discuss  the  different 
tests  which  the  intending  purchaser  of  a  telescope 
should  apply  to  the  instrument. 

The  excellence  of  an  object-glass  can  be  satisfac 
torily  determined  only  by  testing  the  performance 
of  the  telescope  in  the  manner  presently  to  be  de 
scribed.  But  it  is  well  to  examine  the  quality  of 


STRUCTURE   OF    THE   TELESCOPE.  2S 

the  glass  as  respects  transparency  and  uniformity 
of  texture.  Bubbles,  scratches,  and  other  such  de 
fects,  are  not  very  important,  since  they  do  not  affect 
the  distinctness  of  the  field  as  they  would  in  a  Gali 
lean  Telescope, — a  little  light  is  lost,  and  that  is 
all.  The  same  remark  applies  to  dust  upon  the 
glass.  The  glass  should  be  kept  as  free  as  possible 
from  dirt,  damp,  or  dust,  but  it  is  not  advisable  to 
remove  every  speck  which,  despite  such  precaution, 
may  accidentally  fall  upon  the  object-glass.  When 
it  becomes  necessary  to  clean  the  glass,  it  is  to  be 
noted  that  the  substance  used  should  be  soft,  per 
fectly  dry,  and  free  from  dust.  Silk  is  often  recom 
mended,  but  some  silk  is  exceedingly  objectionable 
in  texture, — old  silk,  perfectly  soft  to  the  touch,  is 
perhaps  as  good  as  anything.  If  the  dust  which 
has  fallen  on  the  glass  is  at  all  gritty,  the  glass  will 
suffer  by  the  method  of  cleaning  commonly  adopted, 
in  which  the  dust  is  gathered  up  by  pressure.  The 
proper  method  is  to  clean  a  small  space  near  the 
edge  of  the  glass,  and  to  sweep  from  that  space  as 
centre.  In  this  way  the  dust  is  pushed  before  the 
silk  or  wash-leather,  and  does  not  cut  the  glass.  It 
is  well  always  to  suspect  the  presence  of  gritty  dust, 
and  adopt  this  cautious  method  of  cleaning. 

The  two  glasses  should  on  no  account  be  separated. 

In  examining  an  eye-piece,  the  quality  of  the 
glass  should  be  noted,  and  care  taken  that  both 
glasses  (but  especially  the  field-glass)  are  free  from 
the  least  speck,  scratch,  or  blemish  of  any  kind,  for 
these  defects  will  be  exhibited  in  a  magnified  state 
in  the  field  of  view.  Hence  the  eye-pieces  require 
to  be  as  carefully  preserved  from  damp  and  dust  as 
the  object-glass,  and  to  be  more  frequently  cleaned. 

The  tube  of  the  telescope  should  be  light,  but 
strong,  and  free  from  vibration.  Its  quality  in  the 
last  respect  can  be  tested  by  lightly  striking  it 


24  A    HALF-HOUR    ON   THE 

when  mounted;  the  sound  given  out  should  be 
dead  or  non-resonant.  The  inside  of  the  tube  must 
absorb  extraneous  light,  and  should  therefore  be 
coloured  a  dull  black ;  and  stops  of  varying  radius 
should  be  placed  along  its  length  with  the  same 
object.  Sliding  tubes,  rack-work,  etc.,  should  work 
closely,  yet  easily. 

The  telescope  should  be  well  balanced  for  vision 
with  the  small  astronomical  eye-pieces.  But  as 
there  is  often  occasion  to  use  appliances  which 
disturb  the  balance,  it  is  well  to  have  the  means  of 
at  once  restoring  equilibrium.  A  cord  ring  running 
round  the  tube  (pretty  tightly,  so  as  to  rest  still 
when  the  tube  is  inclined),  and  bearing  a  small 
weight,  will  be  all  that  is  required  for  this  purpose ; 
it  must  be  slipped  along  the  tube  until  the  tube 
is  found  to  be  perfectly  balanced.  Nothing  is  more 
annoying  than,  after  getting  a  star  well  in  the  field, 
to  see  the  tube  shift  its  position  through  defective 
balance,  and  thus  to  have  to  search  again  for  the  star. 
Even  with  such  an  arrangement  as  is  shown  in  fig.  8, 
though  the  tube  cannot  readily  shift  its  position,  it 
is  better  to  have  it  well  balanced. 

The  quality  of  the  stand  has  a  very  important 
influence  on  the  performance  of  a  telescope.  In 
fact,  a  moderately  good  telescope,  mounted  on  a 
steady  stand,  working  easily  and  conveniently,  will 
not  only  enable  the  observer  to  pass  his  time  much 
more  pleasantly,  but  will  absolutely  exhibit  more 
difficult  objects  than 'a  finer  instrument  on  a  rickety, 
ill-arranged  stand.  A  good  observing-chair  is  also 
a  matter  of  some  importance,  the  least  constraint  or 
awkwardness  of  position  detracting  considerably 
from  the  power  of  distinct  vision.  Such,  at  least,  is 
my  own  experience. 

But  the  mere  examination  of  the  glasses,  tube, 
mounting,  &c.,  is  only  the  first  step  in  the  series  of 


STKUCTUKE    OF   THE   TELESCOPE.  25 

tests  which  should  be  applied  to  a  telescope,  since 
the  excellence  of  the  instrument  depends,  not  on  its 
size,  the  beauty  of  its  mounting,  or  any  extraneous 
circumstances,  but  on  its  performance. 

The  observer  should  first  determine  whether  the 
chromatic  aberration  is  corrected.  To  ascertain 
this  the  telescope  should  be  directed  to  the  moon, 
or  (better)  to  Jupiter,  and  accurately  focussed  for 
distinct  vision.  If,  then,  on  moving  the  eye-piece 
towards  the  object-glass,  a  ring  of  purple  appears 
round  the  margin  of  the  object,  and  on  moving  the 
eye-glass  in  the  contrary  direction  a  ring  of  green, 
the  chromatic  aberration  is  corrected,  since  these 
are  the  colours  of  the  secondary  spectrum. 

To  determine  whether  the  spherical  aberration  is 
corrected,  the  telescope  should  be  directed  towards  a 
star  of  the  third  or  fourth  magnitude,  and  focussed 
for  distinct  vision.  A  cap  with  an  aperture  of  about 
one-half  its  diameter  should  then  be  placed  over  the 
object-glass.  If  no  new  adjustment  is  required  for 
distinct  vision,  the  spherical  aberration  is  corrected, 
since  the  mean  focal  length  and  the  focal  length 
of  the  central  rays  are  equal.  If,  when  the  cap  is 
on,  the  eye-piece  has  to  be  pulled  out  for  distinct 
vision,  the  spherical  aberration  has  not  been  fully 
corrected ;  if  the  eye-piece  has  to  be  pushed  in,  the 
aberration  has  been  over-corrected.  As  a  further 
test,  we  may  cut  off  the  central  rays,  by  means  of 
a  circular  card  covering  the  middle  of  the  object- 
glass,  and  compare  the  focal  length  for  distinct 
vision  with  the  focal  length  when  the  cap  is  applied. 
The  extent  of  the  spherical  aberration  may  be  thus 
determined;  but  if  the  first  experiment  gives  a 
satisfactory  result,  no  other  is  required. 

A  star  of  the  first  magnitude  should  next  be 
brought  into  the  field  of  view.  If  an  irradiation 
from  one  side  is  perceived,  part  of  the  object-glass 


26  A    HALF-HOUR    ON   THE 

has  not  the  same  refractive  power  as  the  rest ;  and 
the  part  which  is  defective  can  be  determined  by 
applying  in  different  positions  a  cap  which  hides 
half  the  object-glass.  If  the  irradiation  is  double, 
it  will  probably  be  found  that  the  object-glass  has 
been  too  tightly  screwed,  and  the  defect  will  disap 
pear  when  the  glass  is  freed  from  such  undue  pres 
sure. 

If  the  object-glass  is  not  quite  at  right  angles  to 
the  axis  of  the  tube,  or  if  the  eye-tube  is  at  all  in 
clined,  a  like  irradiation  will  appear  when  a  bright 
star  is  in  the  field.  The  former  defect  is  not  easily 
detected  or  remedied  ;  nor  is  it  commonly  met  with 
in  the  work  of  a  careful  optician.  The  latter  defect 
may  be  detected  by  cutting  out  three  circular  cards 
of  suitable  size  with  a  small  aperture  at  the  centre 
of  each,  and  inserting  one  at  each  end  of  the  eye- 
tube,  and  one  over  the  object-glass.  If  the  tube  is 
rightly  placed  the  apertures  will  of  course  lie  in  a 
right  line,  so  that  it  will  be  possible  to  look  through 
all  three  at  once.  If  not,  it  will  be  easy  to  deter 
mine  towards  what  part  of  the  object-glass  the  eye- 
tube  is  directed,  and  to  correct  the  position  of  the 
tube  accordingly. 

The  best  tests  for  determining  the  defining  power 
of  a  telescope  are  close  double  or  multiple  stars, 
the  components  of  which  are  not  very  unequal. 
The  illuminating  power  should  be  tested  by  direct 
ing  the  telescope  towards  double  or  multiple  stars 
having  one  or  more  minute  components.  Many  of 
the  nebula3  serve  as  tests  both  for  illumination  and 
defining  power.  As  we  proceed  we  shall  meet  with 
proper  objects  for  testing  different  telescopes.  For 
the  present,  let  the  following  list  suffice.  It  is 
selected  from  Admiral  Smyth's  tests,  obtained  by 
diminishing  the  aperture  of  a  6-in.  telescope  having 
a  focal  length  of  8J  feet : 


STRUCTURE    OF    THE    TELESCOPE.  27 

A  two-inch  aperture,  with  powers  of  from  60  to 
100,  should  exhibit 


a  Piscium  (3" -5). 
7  Leonis(3"-2). 


5  Cassiopeise  (9"'5),  mag. 

(4  and  7£). 

Polaris  (18"'6),  mag.  (2J 
' 


A  four-inch,  powers  80  to  120,  should  exhibit 

|  Ursae  Majoris  (2" -4).      I  a  Cassiopeise  (3"-l),  mag. 

(6  and  8). 

7  Ceti(2"'6).  5  Geminorum  (7"-l),  mag. 

|         (4  and  9). 

The  tests  in  the  first  column  are  for  definition, 
those  in  the  second  for  illumination.  It  will  be 
noticed  that,  though  in  the  case  of  Polaris  the 
smaller  aperture  may  be  expected  to  show  the  small 
star  of  less  than  the  9th  magnitude,  a  larger  aper 
ture  is  required  to  show  the  8th  magnitude  compo 
nent  of  cr  Cassiopeiee,  on  account  of  the  greater 
closeness  of  this  double. 

In  favourable  weather  the  following  is  a  good 
general  test  of  the  performance  of  a  telescope: — 
A  star  of  the  3rd  or  4th  magnitude  at  a  consider 
able  elevation  above  the  horizon  should  exhibit  a 
small  well  defined  disc,  surrounded  by  two  or  three 
fine  rings  of  light. 

A  telescope  should  not  be  mounted  within  doors, 
if  it  can  be  conveniently  erected  on  solid  ground,  as 
every  movement  in  the  house  will  cause  the  instru 
ment  to  vibrate  unpleasantly.  Further,  if  the  tele 
scope  is  placed  in  a  warm  room,  currents  of  cold  air 
from  without  will  render  observed  objects  hazy  and 
indistinct.  In  fact,  Sir  W.  Herschel  considered 
that  a  telescope  should  not  even  be  erected  near 
a  house  or  elevation  of  any  kind  round  which  cur 
rents  of  air  are  likely  to  be  produced.  If  a  tele- 


28  A    HALF-HOUB    ON    THE 

scope  is  used  in  a  room,  the  temperature  of  the  room 
should  be  made  as  nearly  equal  as  possible  to  that 
of  the  outer  air. 

When  a  telescope  is  used  out  of  doors  a  '  dew- 
cap,'  that  is,  a  tube  of  tin  or  pasteboard,  some  ten 
or  twelve  inches  long,  should  be  placed.on  the  end 
of  the  instrument,  so  as  to  project  beyond  the 
object-glass.  For  glass  is  a  good  radiator  of  heat, 
so  that  dew  falls  heavily  upon  it,  unless  the  radia 
tion  is  in  some  way  checked.  The  dew-cap  does 
this  effectually.  It  should  be  blackened  within, 
especially  if  made  of  metal.  "  After  use,"  says  old 
Kitchener,  "  the  telescope  should  be  kept  in  a  warm 
place  long  enough  for  any  moisture  on  the  object- 
glass  to  evaporate."  If  damp  gets  between  the 
glasses  it  produces  a  fog  (which  opticians  call  a 
sweat)  or  even  a  seaweed-like  vegetation,  by  which 
a  valuable  glass  may  be  completely  ruined. 

The  observer  should  not  leave  to  the  precious 
hours  of  the  night  the  study  of  the  bearing  and 
position  of  the  objects  he  proposes  to  examine. 
This  should  be  done  by  day — an  arrangement 
which  has  a  twofold  advantage, — the  time  avail 
able  for  observation  is  lengthened,  and  the  eyes  are 
spared  sudden  changes  from  darkness  to  light,  and 
vice  versa.  Besides,  the  eye  is  ill-fitted  to  examine 
difficult  objects,  after  searching  by  candle-light 
amongst  the  minute  details  recorded  in  maps  or 
globes.  Of  the  effect  of  rest  to  the  eye  we  have  an 
instance  in  Sir  J.  Herschel's  rediscovery  of  the 
satellites  of  Uranus,  which  he  effected  after  keeping 
his  eyes  in  darkness  for  a  quarter  of  an  hour. 
Kitchener,  indeed,  goes  so  far  as  to  recommend 
(with  a  crede  experto)  an  interval  of  sleep  in  the 
darkness  of  the  observing-room  before  commencing 
operations.  I  have  never  tried  the  experiment,  but 
I  should  expect  it  to  have  a  bad  rather  than  a  good 


STKUCTUEE    OF    THE    TELESCOPE.  29 

effect  on  the  eyesight,  as  one  commonly  sees  the 
eyes  of  a  person  who  has  been  sleeping  in  his 
day-clothes  look  heavy  and  bloodshot. 

The  object  or  the  part  of  an  object  to  be  observed 
should  be  brought  as  nearly  as  possible  to  the 
centre  of  the  field  of  view.  When  there  is  no  appa 
ratus  for  keeping  the  telescope  pointed  upon  an  object, 
the  best  plan  is  so  to  direct  the  telescope  by  means 
of  the  finder,  that  the  object  shall  be  just  out  of 
the  field  of  view,  and  be  brought  (by  the  earth's 
motion)  across  the  centre  of  the  field.  Thus  the 
vibrations  which  always  follow  the  adjustment  of 
the  tube  will  have  subsided  before  the  object  ap 
pears.  The  object  should  then  be  intently  watched 
during  the  whole  interval  of  its  passage  across  the 
field  of  view. 

It  is  important  that  the  student  should  recognise 
the  fact  that  the  highest  powers  do  not  necessarily 
give  the  best  views  of  celestial  objects.  High 
powers  in  all  cases  increase  the  difficulty  of  obser 
vation,  since  they  diminish  the  field  of  view  and  the 
illumination  of  the  object,  increase  the  motion  with 
which  (owing  to  the  earth's  motion)  the  image 
moves  across  the  field,  and  magnify  all  defects  due 
to  instability  of  the  stand,  imperfection  of  the  ob 
ject-glass,  or  undulation  of  the  atmosphere.  A  good 
object-glass  of  three  inches  aperture  will  in  very 
favourable  weather  bear  a  power  of  about  300,  when 
applied  to  the  observation  of  close  double  or  mul 
tiple  stars,  but  for  all  other  observations  much 
lower  powers  should  be  used.  Nothing  but  failure 
and  annoyance  can  follow  the  attempt  to  employ 
the  highest  powers  on  unsuitable  objects  or  in  un 
favourable  weather. 

The  greatest  care  should  be  taken  in  focussing 
the  telescope.  When  high  powers  are  used  this  is 
a  matter  of  some  delicacy.  It  would  be  well  if  the 


30  A   HALF-HOUR   ON    THE 

eye-pieces  intended  for  a  telescope  were  so  con 
structed  that  when  the  telescope  is  focussed  for  one, 
this  might  be  replaced  by  any  other  without  neces 
sitating  any  use  of  the  focussing  rack-work.  This 
could  be  readily  effected  by  suitably  placing  the 
shoulder  which  limits  the  insertion  of  the  eye 
piece. 

It  will  be  found  that,  even  in  the  worst  weather 
for  observation,  there  are  instants  of  distinct  vision 
(with  moderate  powers)  during  which  the  careful 
observer  may  catch  sight  of  important  details ;  and, 
similarly,  in  the  best  observing  weather,  there  are 
moments  of  unusually  distinct  vision  well  worth 
patient  waiting  for,  since  in  such  weather  alone  the 
full  powers  of  the  telescope  can  be  employed. 

The  telescopist  should  not  be  deterred  from  ob 
servation  by  the  presence  of  fog  or  haze,  since  with 
a  hazy  sky  definition  is  often  singularly  good. 

The  observer  must  not  expect  distinct  vision  of 
objects  near  the  horizon.  Objects  near  the  eastern 
horizon  during  the  time  of  morning  twilight  are 
especially  confused  by  atmospheric  undulations; 
in  fact,  early  morning  is  a  very  unfavourable  time 
for  the  observation  of  all  objects. 

The  same  rules  which  we  have  been  applying  to 
refractors,  serve  for  reflectors.  The  performance  of 
a  reflector  will  be  found  to  differ  in  some  respects, 
however,  from  that  of  a  refractor.  Mr.  Dawes  is, 
we  believe,  now  engaged  in  testing  reflectors,  and 
his  unequalled  experience  of  refractors  will  enable 
him  to  pronounce  decisively  on  the  relative  merits 
of  the  two  classes  of  telescopes. 

We  have  little  to  say  respecting  the  construction 
of  telescopes.  Whether  it  is  advisable  or  not  for 
an  amateur  observer  to  attempt  the  construction  of 
his  own  telescope  is  a  question  depending  entirely 
on  his  mechanical  ability  and  ingenuity.  My 


STKUCTTJKE    OF    THE    TELESCOPE.  31 

own  experience  of  telescope  construction  is  con 
fined  to  the  conversion  of  a  3-feet  into  a  5J-feet 
telescope.  This  operation  involved  some  diffi 
culties,  since  the  aperture  had  to  be  increased  by 
about  an  inch.  I  found  a  tubing  made  of  alternate 
layers  of  card  and  calico  well  pasted  together,  to 
be  both  light  and  strong.  But  for  the  full  length 
of  tube  I  think  a  core  of  metal  is  wanted.  A 
learned  and  ingenious  friend,  Mr.  Sharp,  Fellow  of 
St.  John's  College,  informs  me  that  a  tube  of  tin, 
covered  with  layers  of  brown  paper,  well  pasted 
and  thicker  near  the  middle  of  the  tube,  forms  a 
light  and  strong  telescope-tube,  almost  wholly  free 
from  vibration. 

Suffer  no  inexperienced  person  to  deal  with  your 
object-glass.  I  knew  a  valuable  glass  ruined  by  the 
proceedings  of  a  workman  who  had  been  told  to 
attach  three  pieces  of  brass  round  the  cell  of  the 
double  lens.  What  he  had  done  remained  unknown, 
but  ever  after  a  wretched  glare  of  light  surrounded 
all  objects  of  any  brilliancy. 

One  word  about  the  inversion  of  objects  by  the 
astronomical  telescope.  It  is  singular  that  any 
difficulty  should  be  felt  about  so  simple  a  matter, 
yet  I  have  seen  in  the  writings  of  more  than  one 
distinguished  astronomer,  wholly  incorrect  views  as 
to  the  nature  of  the  inversion.  One  tells  us  that  to 
obtain  the  correct  presentation  from  a  picture  taken 
with  a  telescope,  the  view  should  be  inverted,  held 
up  to  the  light,  and  looked  at  from  the  back  of  the 
paper.  Another  tells  us  to  invert  the  picture  and 
hold  it  opposite  a  looking-glass.  Neither  method 
is  correct.  The  simple  correction  wanted  is  to  hold 
the  picture  upside  down — the  same  change  which 
brings  the  top  to  the  bottom  brings  the  right  to  the 
left,  i.  e.,  fully  corrects  the  inversion. 

In  the  case,  however,  of  a  picture  taken  by  an 


32  A    HALF-HOUR   WITH 

Herschelian  reflector,  the  inversion  not  being  com 
plete,  a  different  method  must  be  adopted.  In  fact, 
either  of  the  above-named  processes,  incorrect  for 
the  ordinary  astronomical,  would  be  correct  for  the 
Herschelian  Telescope.  The  latter  inverts  but 
does  not  reverse  right  and  left ;  therefore  after  in 
verting  our  picture  we  must  interchange  right  and 
left  because  they  have  been  reversed  by  the  inversion. 
This  is  effected  either  by  looking  at  the  picture 
from  behind,  or  by  holding  it  up  to  a  mirror. 


PLATE  11 


i 


+-£. 


« — r: 


\    r"  > 


.•••<;       \^ 
£|L*_. 


s  A4 


£  !       /f 

1^    •". 

rf+\     \  * 


A 


^     I 


.     j  i  -rx.i  «. 

§=dfc^st=ft===3j^^=±± ;- *^1---:  — J*5 


VL  Xo  Zo  V. 


OEION,    LEPUS,   TAURUS,    ETC.  33 


CHAPTER    II. 

A  HALF-HOUR  WITH  ORION,  LEPUS 
TAURUS,  ETC. 

ANY  of  the  half-hours  here  assigned  to  the  con 
stellation-seasons  may  be  taken  first,  and  the  rest  in 
seasonal  or  cyclic  order.  The  following  introductory 
remarks  o.re  applicable  to  each : — 

If  we  stand  on  an  open  space,  on  any  clear  night, 
we  see  above  us  the  celestial  dome  spangled  with 
stars,  apparently  fixed  in  position.  But  after  a  little 
time  it  becomes  clear  that  these  orbs  are  slowly 
shifting  their  position.  Those  near  the  eastern 
horizon  are  rising,  those  near  the  western  setting. 
Careful  and  continuous  observation  would  show  that 
the  stars  are  all  moving  in  the  same  way,  precisely, 
as  they  would  if  they  were  fixed  to  the  concave  sur 
face  of  a  vast  hollow  sphere,  and  this  sphere  rotated 
about  an  axis.  This  axis,  in  our  latitude,  is  inclined 
about  51^°  to  the  horizon.  Of  course  only  one  end 
of  this  imaginary  axis  can  be  above  our  horizon. 
This  end  lies  very  near  a  star  which  it  will  be  well 
for  us  to  become  acquainted  with  at  the  beginning 
of  our  operations.  It  lies  almost  exactly  towards 
the  north,  and  is  raised  from  50°  to  53°  (according 
to  the  season  and  hour)  above  the  horizon.  There 
is  an  easy  method  of  finding  it. 

We  must  first  find  the  Greater  Bear.  It  will  be 
seen  from  Plate  1,  that  on  a  spring  evening  the  seven 
conspicuous  stars  of  this  constellation  are  to  be 
looked  for  towards  the  north-east,  about  half  way 
between  the  horizon  and  the  point  overhead  (or 

D 


34  A   HALF-HOUR    WITH 

zenitJi),  the  length  of  the  set  of  stars  being  vertical. 
On  a  summer's  evening  the  Great  Bear  is  nearly 
overhead.  On  an  autumn  evening  ho  is  towards  the 
north-west,  the  length  of  the  set  of  seven  being  some 
what  inclined  to  the  horizon.  Finally,  on  a  winter's 
evening,  he  is  low  down  towards  the  north,  the 
length  of  the  set  of  seven  stars  being  nearly  in  a 
horizontal  direction. 

Having  found  the  seven  stars,  we  make  use  of  the 
pointers  a  and  (3  (shown  in  Plate  1)  to  indicate 
the  place  of  the  Pole-star,  whose  distance  from  the 
pointer  a  is  rather  more  than  three  times  the  dis 
tance  of  a  from  (3. 

Now  stand  facing  the  Pole-star.  Then  all  the 
stars  are  travelling  round  that  star  in  a  direction  con 
trary  to  that  in  ivhich  the  hands  of  a  watch  move.  Thus 
the  stars  below  the  pole  are  moving  towards  the  right, 
those  above  the  pole  towards  the  left,  those  to  the 
right  of  the  pole  upwards,  those  to  the  left  of  the 
pole  downwards. 

Next  face  the  south.  Then  all  the  stars  on  our 
left,  that  is,  towards  the  east,  are  rising  slantingly 
towards  the  south  ;  those  due  south  are  moving  hori 
zontally  to  the  right,  that  is,  towards  the  west ;  and 
those  on  our  right  are  passing  slantingly  downwards 
towards  the  west. 

It  is  important  to  familiarise  ourselves  with  these 
motions,  because  it  is  through  them  that  objects  pass 
out  of  the  field  of  view  of  the  telescope,  and  by 
moving  the  tube  in  a  proper  direction  we  can  easily 
pick  up  an  object  that  has  thus  passed  away,  whereas 
if  we  are  not  familiar  with  the  varying  motions  in 
different  parts  of  the  celestial  sphere,  we  may  fail 
in  the  attempt  to  immediately  recover  an  object,  and 
waste  time  in  the  search  for  it. 

The  consideration  of  the  celestial  motions  shows 
how  advantageous  it  is,  when  using  an  alt-azimuth, 


DRION,    LEPUS,    TAURUS,    ETC.  35 

to  observe  objects  as  nearly  as  possible  due  south. 
Of  course  in  many  cases  this  is  impracticable,  be 
cause  a  phenomenon  we  wish  to  watch  may  occur 
when  an  object  is  not  situated  near  the  meridian. 
But  in  examining  double  stars  there  is  in  general  no 
reason  for  selecting  objects  inconveniently  situated. 
We  can  wait  till  they  come  round  to  the  meridian, 
and  then  observe  them  more  comfortably.  Besides, 
most  objects  are  higher,  and  therefore  better  seen, 
when  due  south. 

Northern  objects,  and  especially  those  within  the 
circle  of  perpetual  apparition,  often  culminate  (that 
is,  cross  the  meridian,  or  north  and  south  line)  at 
too  great  a  height  for  comfortable  vision.  In  this 
case  we  should  observe  them  towards  the  east  or 
west,  and  remember  that  in  the  first  case  they  are 
rising,  and  in  the  latter  they  are  setting,  and  that  in 
both  cases  they  have  also  a  motion  from  left  to 
right. 

If  we  allow  an  object  to  pass  right  across  the  field 
of  view  (the  telescope  being  fixed),  the  apparent 
direction  of  its  motion  is  the  exact  reverse  of  the 
true  direction  of  the  star's  motion.  This  will  serve 
as  a  guide  in  shifting  the  alt-azimuth  after  a  star 
has  passed  out  of  the  field  of  view. 

The  following  technical  terms  must  be  explained. 
That  part  of  the  field  of  view  towards  which  the  star 
appears  to  move  is  called  the  preceding  part  of  the 
field,  the  opposite  being  termed  the  following  part. 
The  motion  for  all  stars,  except  those  lying  in  an 
oval  space  extending  from  the  zenith  to  the  pole  of 
the  heavens,  is  more  or  less  from  right  to  left  (in 
the  inverted  field).  Now,  if  we  suppose  a  star  to 
move  along  a  diameter  of  the  field  so  as  to  divide  the 
field  into  two  semicircles,  then  in  all  cases  in  which 
this  motion  takes  places  from  right  to  left,  that  semi 
circle  which  contains  the  lowest  point  (apparently) 

D  2 


36  A    HALF-HOUR    WITH 

of  the  field  is  the  northern  half,  the  other  is  the 
southern  half.  Over  the  oval  space  just  mentioned 
the  reverse  holds. 

Thus  the  field  is  divided  into  four  quadrants,  and 
these  are  termed  north  following  (n.  f.\  and  south 
following  (s.  f.J  •  north  preceding  (?i.  p.),  and  souih 
preceding  (s.  p.).  The  student  can  have  no  difficulty 
in  interpreting  these  terms,  since  he  knows  which  is 
the  following  and  which  the  preceding  s  micirde, 
which  the  northern  and  which  the  southern.  In  the 
figures  of  plates  3  and  5,  the  letters  n.  /.,  w.p.,  &c., 
are  affixed  to  the  proper  quadrants.  It  is  to  be  re 
membered  that  the  quadrants  thus  indicated  are 
measured  either  way  from  the  point  and  feather  of 
the  diametral  arrows. 

Next,  of  the  apparent  annual  motion  of  the  stars. 
This  takes  place  in  exactly  the  same  manner  as  the 
daily  motion.  If  we  view  the  sky  at  eight  o'clock 
on  any  day,  and  again  at  the  same  hour  one  month 
later,  we  shall  find  that  at  the  latter  observation  (as 
compared  with  the  former)  the  heavens  appear  to 
have  rotated  by  the  twelfth  part  of  a  complete  cir 
cumference,  and  the  appearance  presented  is  pre 
cisely  the  same  as  we  should  have  observed  had  we 
waited  for  two  hours  (the  twelfth  part  of  a  day)  on 
the  day  of  the  first  observation. 


Our  survey  of  the  heavens  is  supposed  to  be  com 
menced  during  the  first  quarter  of  the  year,  at  ten 
o'clock  on  the  20th  of  January,  or  at  nine  on  the 
5th  of  February,  or  at  eight  on  the  19th  of  Feb 
ruary,  or  at  seven  on  the  tith  of  March,  or  at  hours 
intermediate  to  these  on  intermediate  days. 

We  look  first  for  the  Great  Bear  towards  the 
north-east,  as  already  described,  and  thence  find  the 
Pole-star;  turning  towards  which  we  see,  towards 


OKION,    LEPUS,    TAURUS,    ETC.  37 

the  right  and  downwards,  the  two  guardians  of  the 
pole  (J3  and  y  UrsaB  Minoris).  Immediately  under 
the  Pole-star  is  the  Dragon's  Head,  a  conspicuous 
diamond  of  stars.  Just  on  the  horizon  is  Vega, 
scintillating  brilliantly.  Overhead  is  the  brilliant 
Capella,  near  which  the  Milky  Way  is  seen  passing 
down  to  the  horizon  on  either  side  towards  the 
quarters  S.S.E.  and  N.N.W. 

For  the  present  our  business  is  with  the  southern 
heavens,  however. 

Facing  the  south,  we  see  a  brilliant  array  of  stars, 
Sirius  unmistakeably  over  shining  the  rest.  Orion 
is  shining  in  full  glory,  his  leading  brilliant,  Betel- 
geuse  *  being  almost  exactly  on  the  meridian,  and 
also  almost  exactly  half  way  between  the  horizon 
and  the  zenith.  In  Plate  2  is  given  a  map  of  this 
constellation  and  its  neighbourhood. 

Let  us  first  turn  the  tube  on  Sirius.  It  is  easy 
to  get  him  in  the  field  without  the  aid  of  a  finder. 
The  search  will  serve  to  illustrate  a  method  often 
useful  when  a  telescope  has  no  finder.  Having 
taking  out  the  eye-piece  — a  low-power  one,  suppose 
— direct  the  tube  nearly  towards  Sirius.  On  looking 
through  it,  a  glare  of  light  will  be  seen  within  the 
tube.  Now,  if  the  tube  be  slightly  moved  about,  the 
light  will  be  seen  to  wax  and  wane,  according  as 
the  tube  is  more  or  less  accurately  directed.  Fol 
lowing  these  indications,  it  will  be  found  easy  to 
direct  the  tube,  so  that  the  object-glass  shall  appear 
full  of  light.  When  this  is  done,  insert  the  eye 
piece,  and  the  star  will  be  seen  in  the  field. 

But  the  telescope  is, out  of  focus,  therefore  we 
must  turn  the  small  focussing  screw.  Observe  the 

*  Betelgeuse— commonly  intei-preted  the  Giant's  Shoulder 
— il)t-al-jauza.  The  words,  however,  really  signify,  '-the 
armpit  of  the  central  one,"  Orion  being  so  named,  because 
he  is  divided  centrally  by  the  equator. 


38  A    HALF-HOUR    WITH 

charming  chromatic  changes — green,  and  red,  and 
blue  light,  purer  than  the  hues  of  the  rainbow,  scin 
tillating  and  coruscating  with  wonderful  brilliancy. 
As  we  get  the  focus,  the  excursions  of  these  light 
flashes  diminish  until — if  the  weather  is  favourable 
— -the  star  is  seen,  still  scintillating,  and  much 
brighter  than  to  the  naked  eye,  but  reduced  to  a 
small  disc  of  light,  surrounded  (in  the  case  of  so 
bright  a  star  as  Sirius)  with  a  slight  glare.  If  after 
obtaining  the  focus  the  focussing  rackwork  be  still 
turned,  we  see  a  coruscating  image  as  before.  In 
the  case  of  a  very  brilliant  star  these  coruscations 
are  so  charming  that  we  may  be  excused  for  calling 
the  observer's  attention  to  them.  The  subject  is 
not  without  interest  and  difficulty  as  an  optical  one. 
But  the  astronomer's  object  is  to  get  rid  of  all 
these  flames  and  sprays  of  coloured  light,  so  that  he 
has  very  little  sympathy  with  the  admiration  which 
Wordsworth  is  said  to  have  expressed  for  out-of-focus 
views  of  the  stars. 

We  pass  to  more  legitimate  observations,  noticing 
in  passing  that  Sirius  is  a  double  star,  the  com 
panion  being  of  the  tenth  magnitude,  and  distant 
about  ten  seconds  from  the  primary.  But  our  be 
ginner  is  not  likely  to  see  the  companion,  which  is 
a  very  difficult  object,  owing  to  the  overpowering 
brilliancy  of  the  primary. 

Orion  affords  the  observer  a  splendid  field  of  re 
search.  It  is  a  constellation  rich  in  double  and 
multiple  stars,  clusters,  and  nebulae.  We  will  begin 
with  an  easy  object. 

The  star  8  (Plate  3),  or  Jffofofa,  the  uppermost 
of  the  three  stars  forming  the  belt,  is  a  wide  double. 
The  primary  is  of  the  second  magnitude,  the  secon 
dary  of  the  seventh,  both  being  white. 

The  star  a  (Betelgeuse)  is  an  interesting  object,  on 
account  of  its  colour  and  brilliance,  and  as  one  of 


ORION,    LEPUS,    TAURUS,    ETC.  39 

the  most  remarkable  variables  in  the  heavens.  It  was 
first  observed  to  be  variable  by  Sir  John  Herschel 
in  1836.  At  this  period  its  variations  were  "  most 
marked  and  striking."  This  continued  until  1840, 
when  the  changes  became  "  much  less  conspicuous. 
In  January,  1849,  they  had  recommenced,  and  on 
December  5th,  1852,  Mr.  Fletcher  observed  a  Orionis 
brighter  than  Capella,  and  actually  the  largest  star 
in  the  northern  hemisphere."  That  a  star  so  con 
spicuous,  and  presumably  so  large,  should  present 
such  remarkable  variations,  is  a  circumstance  which 
adds  an  additional  interest  to  the  results  which  have 
rewarded  the  spectrum-analysis  of  this  star  by  Mr. 
Huggins  and  Professor  Miller.  It  appears  that 
there  is  decisive  evidence  of  the  presence  in  this 
luminary  of  many  elements  known  to  exist  in  our  own 
sun ;  amongst  others  are  found  sodium,  magnesium, 
calcium,  iron,  and  bismuth.  Hydrogen  appears  to 
be  absent,  or,  more  correctly,  there  are  no  lines  in 
the  star's  spectrum  corresponding  to  those  of  hy 
drogen  in  the  solar  spectrum.  Secchi  considers  that 
there  is  evidence  of  an  actual  change  in  the  spectrum 
of  the  star,  an  opinion  in  which  Mr.  Huggins  does 
not  coincide.  In  the  telescope  Betelgeuse  appears 
as  "  a  rich  and  brilliant  gem,"  says  Lassoll,  "  a  rich 
topaz,  in  hue  and  brilliancy  differing  from  any  that 
I  have  seen." 

Turn  next  to  /5  (Rigel),  the  brightest  star  below 
the  belt.  This  is  a  very  noted  double,  and  will 
severely  test  our  observer's  telescope,  if  small.  The 
components  are  well  separated  (see  Plate  3),  com 
pared  with  many  easier  doubles;  the  secondary  is 
also  of  the  seventh  magnitude,  so  that  neither  as 
respects  closeness  nor  smallness  of  the  secondary, 
is  Rigel  a  difficult  object.  It  is  the  combination 
of  the  two  features  which  makes  it  a  test-object. 
Kitchener  says  a  1 J  -  inch  object-glass  should  show 


10  A    HALF-HOUR    WITH 

Kigcl  double;  in  earlier  editions  of  his  work  he 
gave  2^-inches  as  the  necessary  aperture.  Smyth 
mentions  Kigcl  as  a  test  for  a  4-inch  aperture,  with 
powers  of  from  80  to  120.  A  3-inch  aperture,  how 
ever,  will  certainly  show  the  companion.  Eigel  is 
iiu  orange  star,  the  companion  blue. 

Turn  next  to  A.  the  northernmost  of  the  set  of 
three  stars  in  the  head  of  Orion.  This  is  a  triple 
star,  though  an  aperture  of  3  inches  will  show  it 
only  as  a  double.  The  components  are  5"  apart, 
the  colours  pale  white  and  violet.  With  the  full 
powers  of  a  3^-inch  glass  a  faint  companion  may  be 
seen  above  A.. 

The  star  £,  the  lowest  in  the  belt,  may  be  tried 
with  a  3^-inch  glass.  It  is  a  close  double,  the 
components  being  nearly  equal,  and  about  2?r"  apart 
(see  Plate  3). 

For  a  change  we  will  now  try  our  telescope  on  a 
nebula,  selecting  the  great  nebula  in  the  Sword. 
The  place  of  this  object  is  indicated  in  Plate  2. 
There  can  be  no  difficulty  in  finding  it  since  it  is 
clearly  visible  to  the  naked  eye  on  a  moonless 
night  —the  only  sort  of  night  on  which  an  observer 
would  care  to  look  at  nebulae.  A  low  power  should 
be  employed. 

The  nebula  is  shown  in  Plate  3  as  I  have  seen 
it  with  a  3-inch  aperture.  We  see  nothing  of  those 
complex  streams  of  light  which  are  portrayed  in 
the  drawings  of  Ilerschcl,  Bond,  and  Lassell,  but 
enough  to  excite  our  interest  and  wonder.  What 
is  this  marvellous  light-cloud?  One  could  almost 
imagine  that  there  was  a  strange  prophetic  meaning 
in  the  words  which  have  been  translated  "  Canst 
thou  loose  the  bands  of  Orion?"  Telescope  after 
telescope  had  been  turned  on  this  wonderful  object 
with  the  hope  of  resolving  its  light  into  stars.  But 
it  proved  intractable  to  Herschel's  great  reflector,  to 


OlilON,    LEPUS,    TAURUS,    ETC.  41 

Lassell's  2-feet  reflector,  to  Lord  Eosse's  3-feet 
reflector,  and  even  partially  to  the  great  6-feet  re 
flector.  Then  we  hear  of  its  supposed  resolution 
into  stars,  Lord  Rosse  himself  writing  to  Professor 
Nichol,  in  1846,  "I  may  safely  say  there  can  be 
little,  if  any,  doub't  as  to  the  resolvability  of  the 
nebula  ; — all  about  the  trapezium  is  a  mass  of  stars, 
the  rest  of  the  nebula  also  abounding  with  stars,  and 
exhibiting  the  characteristics  of  resolvability  strongly 
marked." 

It  was  decided,  therefore,  that  assuredly  the  great 
nebula  is  a  congeries  of  stars,  and  not  a  mass  of 
nebulous  matter  as  had  been  surmised  by  Sir  W. 
Herschel.  And  therefore  astronomers  were  not  a 
little  surprised  when  it  was  proved  by  Mr.  Huggins' 
spectrum-analysis  that  the  nebula  consists  of  gaseous 
matter.  How  widely  extended  this  gaseous  uni 
verse  may  be  we  cannot  say.  The  general  opinion 
is  that  the  nebulae  are  removed  far  beyond  the  fixed 
stars.  If  this  were  so,  the  dimensions  of  the  Orion 
nebula  would  be  indeed  enormous,  far  larger  pro 
bably  than  those  of  the  whole  system  whereof  our 
sun  is  a  member.  I  believe  this  view  is  founded  on 
insufficient  evidence,  but  this  would  not  be  the  place 
to  discuss  the  subject.  I  shall  merely  point  out 
that  the  nebula  occurs  in  a  region  rich  in  stars,  and 
if  it  is  not,  like  the  great  nebula  in  Argo,  clustered 
around  a  remarkable  star,  it  is  found  associated  in 
a  manner  which  I  cannot  look  upon  as  accidental 
with  a  set  of  small-magnitude  stars,  and  notably 
with  the  trapezium  which  surrounds  that  very  re 
markable  black  gap  within  the  nebula.  The  fact 
that  the  nebula  shares  the  proper  motion  of  the 
trapezium  appears  inexplicable  if  the  nebula  is 
really  far  out  in  space  beyond  the  trapezium.  A 
very  small  proper  motion  of  the  trapezium  (alone) 
would  long  since  have  destroyed  the  remarkable 


42  A    HALF-HOUR    WITH 

agreement  in  the  position  of  the  dark  gap  and  the 
trapezium  which  has  been  noticed  for  so  many  years. 

But  whether  belonging  to  our  system  or  far  be 
yond  it,  the  great  nebula  must  have  enormous 
dimensions.  A  vast  gaseous  system  it  is,  sustained 
by  what  arrangements  or  forces  we  cannot  tell,  nor 
can  we  know  what  purposes  it  subserves.  Mr.  Hug- 
gins'  discovery  that  comets  have  gaseous  nuclei, 
(so  far  as  the  two  he  has  yet  examined  show)  may 
suggest  the  speculation  that  in  the  Orion  nebula  we 
see  a  vast  system  of  comets  travelling  in  extensive 
orbits  around  nuclear  stars,  and  so  slowly  as  to 
exhibit  for  long  intervals  of  time  an  unchanged 
figure.  "  But  of  such  speculations "  we  may  say 
with  Sir  J.  Herschel  "  there  is  no  end." 

To  return  to  our  telescopic  observations: — The 
trapezium  aifords  a  useful  test  for  the  light-gathering 
power  of  the  telescope.  Large  instruments  exhibit 
nine  stars.  But  our  observer  may  be  well  satisfied 
with  his  instrument  and  his  eye-sight  if  he  can  see 
five  with  a  3^-inch  aperture.*  A  good  3-inch  glass 
shows  four  distinctly.  But  with  smaller  apertures 
only  three  are  visible. 

The  whole  neighbourhood  of  the  great  nebula 
will  well  repay  research.  The  observer  may  sweep 
over  it  carefully  on  any  dark  night  with  profit. 
Above  the  nebula  is  the  star-cluster  362  H.  The 
star  i  ( double  as  shown  in  Plate  3 )  below  the 
nebula  is  involved  in  a  strong  nebulosity.  And  in 
searching  over  this  region  we  meet  with  delicate 
double,  triple,  and  multiple  stars,  which  make  the 
survey  interesting  with  almost  any  power  that  may 
be  applied. 

Above  the  nebula  is  the  star  o-,  a  multiple  star. 

*  I  have  never  been  able  to  see  more  than  four  with  a 
Gf-inch  aperture.  I  give  a  view  of  the  trapezium  as  seen 
with  an  8 -inch  equatorial. 


ORION,    LEPUS,    TAURUS,    ETC.  43 

To  an  observer  with  a  good  3^-inch  glass  a-  appears 
as  an  octuple  star.  It  is  well  seen,  however,  as  a 
fine  multiple  star  with  a  smaller  aperture.  Some  of 
the  stars  of  this  group  appear  to  be  variable. 

The  star  p  Orionis  is  an  unequal,  easy  double,  the 
components  being  separated  by  nearly  seven  seconds. 
The  primary  is  orange,  the  smaller  star  smalt-blue 
(see  Plate  3). 

The  middle  star  of  the  belt  (e)  has  a  distant  blue 
companion.  This  (star,  like  t,  is  nebulous.  In  fact, 
the  whole  region  within  the  triangle  formed  by 
stars  y,  /c,  and  /3  is  full  of  nebulous  double  and  mul 
tiple  stars,  whose  aggregation  in  this  region  I  do 
not  consider  wholly  accidental. 

We  have  not  explored  half  the  wealth  of  Orion, 
but  leave  much  for  future  observation.  We  must 
turn,  however,  to  other  constellations. 

Below  Orion  is  Lepus,  the  Hare,  a  small  con 
stellation  containing  some  remarkable  doubles. 
Among  these  vse  may  note  £,  a  white  star  with  a 
scarlet  companion ;  y,  a  yellow  and  garnet  double ; 
and  i,  a  double  star,  white  and  pale  violet,  with 
a  distant  red  companion.  The  star  K  Leporis  is  a 
rather  close  double,  white  with  a  small  green  compa 
nion.  The  intensely  red  star  E  Leporis  (a  variable) 
will  be  found  in  the  position  indicated  in  the  map. 

Still  keeping  within  the  boundary  of  our  map, 
we  may  next  turn  to  the  fine  cluster  2  H  (vii.)  in 
Monoceros.  This  cluster  is  visible  to  the  naked 
eye,  and  will  be  easily  found.  The  nebula  2  H  (iv.) 
is  a  remarkable  one  with  a  powerful  telescope. 

The  star  1 1  Monocerotis  is  a  fine  triple  star  de 
scribed  by  the  elder  Herschel  as  one  of  the  finest 
sights  in  the  heavens.  Our  observer,  however,  will 
see  it  as  a  double  (see  Plate  3).  8  Monocerotis  is 
an  easy  double,  yellow  and  lavender. 

We  may  now  leave  the  region  covered  by  the 


44  A    HALF-HOUR   WITH 

map  and  take  a  survey  of  the  heavens  for  some 
objects  well  seen  at  this  season. 

Towards  the  south-east,  high  up  above  the 
horizon,  we  see  the  twin-stars  Castor  and  Pollux. 
The  upper  is  Castor,  the  finest  double  star  visible 
in  the  northern  heavens.  The  components  are 
nearly  equal  and  rather  more  than  5"  apart  (see 
Plate  3).  Both  are  white  according  to  the  best 
observers,  but  the  smaller  is  thought  by  some  to  be 
slightly  greenish. 

Pollux  is  a  coarse  but  fine  triple  star  (in  large 
instruments  multiple).  The  components  orange, 
grey,  and  lilac. 

There  are  many  other  fine  objects  in  Gemini,  but 
we  pass  to  Cancer. 

The  fine  cluster  Praesepe  in  Cancer  may  easily  be 
found  as  it  is  distinctly  visible  to  the  naked  eye  in 
the  position  shown  in  Plate  1,  Map  I.  In  the 
telescope  it  is  seen  as  shown  in  Plate  3. 

The  star  i  Cancri  is  a  wide  double,  the  colours 
orange  and  blue. 

Procyon,  the  first-magnitude  star  between  Prae- 
sepe  and  Sinus,  is  finely  coloured — yellow  with  a 
distant  orange  companion,  which  appears  to  be 
variable. 

Below  the  Twins,  almost  in  a  line  with  them,  is  the 
star  a  Hydros,  called  Al  Fard,  or  "  the  Solitary  One." 
It  is  a  2nd  magnitude  variable.  I  mention  it,  how 
ever,  not  on  its  own  account,  but  as  a  guide  to  the 
fine  double  e  Hydras.  This  star  is  the  middle  one 
of  a  group  of  three,  lying  between  Pollux  and  Al 
Fard  rather  nearer  the  latter.  The  components  of 
e  HydraB  are  separated  by  about  3^"  (see  Plate  3). 
The  primary  is  of  the  fourth,  the  companion  of 
the  eighth  magnitude;  the  former  is  yellow,  the 
latter  a  ruddy  purple.  The  period  of  €  Hydra  is 
about  450  years. 


ORION,    LEPUS,    TAUHUS,    ETC.  45 

The  constellation  Leo  Minor,  now  due  east  and 
about  midway  between  the  horizon  and  the  zenith, 
is  well  worth  sweeping  over.  I't  contains  several 
fine  fields. 

Let  us  next  turn  to  the  western  heavens.  Here 
there  are  some  noteworthy  objects. 

To  begin  with,  there  are  the  Pleiades,  showing  to 
the  naked  eye  only  six  or  seven  stars.  In  the 
telescope  the  Pleiades  appear  as  shown  in  Plate  3. 

The  Hyades  also  show  some  fine  fields  with  low 
powers.  » < 

Aldebaran,  the  principal  star  of  the  Hyades,  as 
also  of  the  constellation  Taurus,  is  a  noted  red  star. 
It  is  chiefly  remarkable  for  the  close  spcctroscopic 
analysis  to  which  it  has  been  subjected^  by  Messrs. 
Huggins  and  Miller.  Unlike  Betelgeuse,  the  spec 
trum  of  Aldebaran  exhibits  the  lines  corresponding 
to  hydrogen,  and  no  less  than  eight  metals — sodium, 
magnesium,  calcium,  iron,  bismuth,  tellurium,  anti 
mony,  and  mercury,  are  proved  to  exist  in  the  con 
stitution  of  this  brilliant  red  star. 

On  the  right  of  Aldebaran,  in  the  position  indi 
cated  in  Plate  1,  Map  I.,  are  the  stars  £  and  j3 
Tauri.  If  with  a  low  power  the  observer  sweep 
from  £  towards  /?,  he  will  soon  find — not  far  from  £ 
(at  a  distance  of  about  one-sixth  of  the  distance 
separating  /5  from  £),  the  celebrated  Crab  nebula, 
known  as  1  M.  This  was  the  first  nebula  discovered 
by  Messier,  and  its  discovery  led  to  the  formation  of 
his  catalogue  of  103  nebulae.  In  a  small  telescope 
this  object  appears  as  a  nebulous  light  of  oval  form, 
no  traces  being  seen  of  the  wisps  and  sprays  of 
light  presented  in  Lord  Rosse's  well  known  picture 
of  the  nebula. 

Here  I  shall  conclude  the  labours  of  our  first 
half-hour  among  the  stars,  noticing  that  the  exami 
nation  of  Plate  1  will  show  what  other  constella- 


46  A    HALF-HOUR    WITH 

tions  besides  those  here  considered  are  well  situated 
for  observation  at  this  season.  It  will  be  remarked 
that  many  constellations  well  seen  in  the  third  half- 
hour  (Chapter  IV.)  are  favourably  seen  in  the  first 
also,  and  vice  versa.  For  instance,  the  constellation 
Ursa  Major  well-placed  towards  the  north-east  in 
the  first  quarter  of  the  year,  is  equally  well-placed 
towards  the  north-west  in  the  third,  and  similarly 
of  the  constellation  Cassiopeia.  The  same  relation 
connects  the  second  and  fourth  quarters  of  the 
year. 


PLATE  m. 


8  Orion's  t-  Oriormj  e,  Orkmis 


£  Orionie  #  Mcmoeerotis      £,  Hvdrae  Castor  Trapezii 


G*:  Kebula.  m  Ox-ion 


£Lyrac      ..  7  Lyrae  $  Hferculis  Y  Hei'culis  allerculis 


LYRA,    HERCULES,    CORVUS,    CRATER,    ETC.  47 


CHAPTEE    III. 

A  HALF-HOUR  WITH  LYEA,  HERCULES,  COEVUS, 
CRATER,  ETC. 

THE  observations  now  to  be  commenced  are  sup 
posed  to  take  place  during  the  second  quarter  of  the 
year, — at  ten  o'clock  on  the  20th  of  April,  or  at 
nine  on  the  5th  of  May,  or  at  eight  on  the  21st  of 
May,  or  at  seven  on  the  5th  of  June,  or  at  hours 
intermediate  to  these  on  intermediate  days. 

We  again  look  first  for  the  Great  Bear,  now  near 
the  zenith,  and  thence  find  the  Pole-star.  Turning 
towards  the  north,  we  see  Cassiopeia  between  the 
Pole-star  and  the  horizon.  Towards  the  north-west 
is  the  brilliant  Capella,  and  towards  the  north-east 
the  equally  brilliant  Vega,  beneath  which,  and  some 
what  northerly,  is  the  cross  in  Cygnus.  The  Milky 
Way  passes  from  the  eastern  horizon  towards  the 
north  (low  down),  and  so  round  to  the  western 
horizon. 

In  selecting  a  region  for  special  observation,  we 
shall  adopt  a  different  plan  from  that  used  in  the 
preceding  "  half-hour."  The  region  on  the  equator 
and  towards  the  south  is  indeed  particularly  inter 
esting,  since  it  includes  the  nebular  region  in  Virgo. 
Within  this  space  nebulae  are  clustered  more  closely 
than  over  any  corresponding  space  in  the  heavens, 
save  only  the  greater  Magellanic  cloud.  But  to  the 
observer  with  telescopes  of  moderate  power  these 
nebulae  present  few  features  of  special  interest ;  and 
there  are  regions  of  the  sky  now  well  situated  for 
observation,  which,  at  most  other  epochs  are  either 


48  A   HALF-HOUK    WITH 

low  down  towards  the  horizon  or  inconveniently 
near  to  the  zenith.  We  shall  therefore  select  one 
of  these,  the  region  included  in  the  second  map  of 
Plate  2,  and  the  neighbouring  part  of  the  celestial 
sphere. 

At  any  of  the  hours  above  named,  the  constel 
lation  Hercules  lies  towards  the  east.  A  quadrant 
taken  from  the  zenith  to  the  eastern  horizon  passes 
close  to  the  last  star  (?;)  of  the  Great  Bear's  tail, 
through  /?,  a  star  in  Bootes'  head,  near  ft  Herculis, 
between  the  two  "Alphas"  which  mark  the  heads 
of  Hercules  and  Ophiuchus,  and  so  past  ft  Ophiuchi, 
a  third-magnitude  star  near  the  horizon.  And  here 
we  may  turn  aside  for  a  moment  to  notice  the 
remarkable  vertical  row  of  six  conspicuous  stars 
towards  the  east-south-east;  these  are,  counting 
them  in  order  from  the  horizon,  £,  e,  and  S  Ophiuchi, 
e,  a,  and  8  Serpentis. 

Let  the  telescope  first  be  directed  towards  Vega. 
This  orb  presents  a  brilliant  appearance  in  the  tele 
scope.  Its  colour  is  a  bluish-white.  In  an  ordi 
nary  telescope  Vega  appears  as  a  single  star,  but 
with  a  large  object-glass  two  distant  small  com 
panions  are  seen.  A  nine-inch  glass  shows  also 
two  small  companions  within  a  few  seconds  of  Vega. 
In  the  great  Harvard  refractor  Vega  is  seen  with 
no  less  than  thirty-five  companions.  I  imagine 
that  all  these  stars,  and  others  which  can  be 
seen  in  neighbouring  fields,  indicate  the  associa 
tion  of  Vega  with  the  neighbouring  stream  of  the 
Milky  Way. 

Let  our  observer  now  direct  his  telescope  to  the 
star  e  Lyraa.  Or  rather,  let  him  first  closely  ex 
amine  this  star  with  the  naked  eye.  The  star  is 
easily  identified,  since  it  lies  to  the  left  of  Vega, 
forming  with  £  a  small  equilateral  triangle.  A  care 
ful  scrutiny  suffices  to  indicate  a  peculiarity  in  this 


LYRA,  HERCULES,  OORVU8,  CRATER,  ETC.     49 

star.  If  our  observer  possesses  very  good  eye-sight, 
he  will  distinctly  recognise  it  as  a  "  naked-eye 
double";  but  more  probably  he  will  only  notice 
that  it  appears  lengthened  in  a  north  and  south 
direction.*  In  the  finder  the  star  is  easily  divided. 
Applying  a  low  power  to  the  telescope  itself,  we 
see  e  Lyrse  as  a  wide  double,  the  line  joining  the 
components  lying  nearly  north  and  south.  The 
southernmost  component  (the  upper  in  the  figure) 
is  called  e1,  the  other  e2.  Seen  as  a  double,  both 
components  appear  white. 

Now,  if  the  observer's  telescope  is  sufficiently 
powerful,  each  of  the  components  may  be  seen  to 
be  itself  double.  First  try  e1,  the  northern  pair. 
The  line  joining  the  components  is  directed  as 
shown  in  Plate  3.  The  distance  between  them  is 
3"- 2,  their  magnitudes  5  and  6^,  and  their  colours 
yellow  and  ruddy.  If  the  observer  succeeds  in 
seeing  e1  fairly  divided,  he  will  probably  not  fail 
in  detecting  the  duplicity  of  c2,  though  this  is  a 
rather  closer  pair,  the  distance  between  the  com 
ponents  being  only  2"'6.  The  magnitudes  are  5 
and  5^,  both  being  white.  Between  e1  and  e2  are 
three  faint  stars,  possibly  forming  with  the  quad 
ruple  a  single  system. 

Let  us  next  turn  to  the  third  star  of  the  equi 
lateral  triangle  mentioned  above — viz.  to  the  star 
£  Lyras.  This  is  a  splendid  but  easy  double.  It 
is  figured  in  Plate  3,  but  it  must  be  noticed  that 


*  Sir  W.  Herschel  several  times  saw  €  Lyrse  sis  a  double. 
Bessel  also  relates  that  when  he  was  a  lad  of  thirteen  he 
could  see  this  star  double.  I  think  persons  having  average 
eye-sight  could  see  it  double  if  they  selected  a  suitable 
hour  for  observation.  My  own  eye-sight  is  not  good  enough 
for  this,  but  I  can  distinctly  see  this  star  wedged  whenever 
the  line  joining  the  components  is  inclined  about  45°  to  the 
horizon,  and  also  when  Lyra  is  near  the  zenith. 

E 


50  A   HALF-HOUR    WITH 

the  figure  of  £  and  the  other  nine  small  figures  are 
not  drawn  on  the  same  scale  as  e  Lyrae.  The  actual 
distance  between  the  components  of  £  Lyra  is 
44",  or  about  one-fourth  of  the  distance  separating 
e1  from  e2.  The  components  of  £  are  very  nearly 
equal  in  magnitude,  in  colour  topaz  and  green,  the 
topaz  component  being  estimated  as  of  the  fifth  mag 
nitude,  the  green  component  intermediate  between 
the  fifth  and  sixth  magnitudes. 

We  may  now  turn  to  a  star  not  figured  in  the 
map,  but  readily  found.  It  will  be  noticed  that 
the  stars  e,  a,  ft,  and  y  form,  with  two  small  stars 
towards  the  left,  a  somewhat  regular  hexagonal 
figure— a  hexagon,  in  fact,  having  three  equal  long 
sides  and  three  nearly  equal  short  sides  alternating 
with  the  others.  The  star  ^  Lyrae  forms  the  angle 
next  to  e.  It  is  a  wide  and  unequal  double,  as 
figured  in  Plate  3.  The  larger  component  is  azure 
blue  ;  the  smaller  is  violet,  and,  being  only  of  the 
ninth  magnitude,  is  somewhat  difficult  to  catch  with 
apertures  under  3  inches. 

The  star  S2  Lyree  is  orange,  S1  blue.  In  the  same 
field  with  these  are  seen  many  other  stars. 

The  stars  y1  and  y2  may  also  be  seen  in  a  single 
field,  the  distance  between  them  being  about  half 
the  moon's  mean  diameter.  The  former  is  quadruple, 
the  components  being  yellow,  bluish,  pale  blue,  and 
blue. 

Turn  next  to  the  stars  ft  and  y  Lyrae,  the  former 
a  multiple,  the  latter  an  unequal  double  star.  It  is 
not,  however,  in  these  respects  that  these  stars  are 
chiefly  interesting,  but  for  their  variability.  The 
variability  of  y  has  not  indeed  been  fully  esta 
blished,  though  it  is  certain  that,  having  once  been 
less  bright,  y  is  now  considerably  brighter  than  ft. 
The  change,  however,  may  be  due  to  the  variation  of 
ft  alone.  This  star  is  one  of  the  most  remarkable 


LYRA,  HERCULES,  CORVUS,  CRATEH,  ETC.     51 

variables  known.  Its  period  is  12d.  21h.  53m.  10s. 
In  this  time  it  passes  from  a  maximum  brilliancy — 
that  of  a  star  of  the  3-4  magnitude — to  a  minimum 
lustre  equal  to  that  of  a  star  of  the  4*3  magnitude, 
thence  to  the  same  maximum  brilliancy  as  before, 
thence  to  another  minimum  of  lustre— that  of  a  star 
of  the  4*5  magnitude — and  so  to  its  maximum  lustre 
again,  when  the  cycle  of  changes  recommences. 
These  remarkable  changes  seem  to  point  to  the  ex 
istence  of  two  unequal  dark  satellites,  whose  dimen 
sions  bear  a  much  greater  proportion  to  those  of 
the  bright  components  of  (3  Lyras  than  the  dimen 
sions  of  the  members  of  the  Solar  System  bear  to 
those  of  the  sun.  In  this  case,  at  any  rate,  the 
conjecture  hazarded  about  Algol,  that  the  star  re 
volves  around  a  dark  central  orb,  would  be  insuffi 
cient  to  account  for  the  observed  variation. 

Nearly  midway  between  (3  and  y  lies  the  won 
derful  ring-nebula  57  M,  of  which  an  imperfect  idea 
will  be  conveyed  by  the  last  figure  of  Plate  3.  This 
nebula  was  discovered  in  1772,  by  Darquier,  at 
Toulouse.  It  is  seen  as  a  ring  of  light  with  very 
moderate  telescopic  power.  In  a  good  3^-inch  tele 
scope  the  nebula  exhibits  a  mottled  appearance  and 
a  sparkling  light.  Larger  instruments  exhibit  a 
faint  light  within  the  ring ;  and  in  Lord  Kosse's 
great  Telescope  "wisps  of  stars"  are  seen  within, 
and  faint  streaks  of  light  stream  from  the  outer 
border  of  the  ring.  This  nebula  has  been  subjected 
to  spectrum-analysis  by  Mr.  Huggins.  It  turns  out 
to  be  a  gaseous  nebula !  In  fact,  ring-nebulas— of 
which  only  seven  have  been  detected— seem  to  be 
long  to  the  same  class  as  the  planetary  nebulas,  all 
of  which ,  exhibit  the  line-spectrum  indicative  of 
gaseity.  The  brightest  of  the  three  lines  seen  in 
the  spectrum  of  the  ring-nebula  in  Lyra  presents 
a  rather  peculiar  appearance,  "  since  it  consists,'1 

E  2 


52  A    HALF-HOUR    WITH 

says  Mr.  Huggins,  "  of  two  bright  dots,  correspond 
ing  to  sections  of  the  ring,  and  between  these  there 
is  not  darkness,  but  an  excessively  faint  line  joining 
them.  This  observation  makes  it  probable  that  the 
faint  nebulous  matter  occupying  the  central  portion 
is  similar  in  constitution  to  that  of  the  ring." 

The  constellation  Hercules  also  contains  many 
very  interesting  objects.  Let  us  first  inspect  a 
nebula  presenting  a  remarkable  contrast  with  that 
just  described.  I  refer  to  the  nebula  13  M,  known 
as  Halley's  nebula  (Plate  3).  This  nebula  is  visible 
to  the  naked  eye,  and  in  a  good  telescope  it  is  a  most 
wonderful  object  :  "  perhaps  no  one  ever  saw  it  for 
the  first  time  without  uttering  a  shout  of  wonder." 
It  requires  a  very  powerful  telescope  completely  to 
resolve  this  fine  nebula,  but  the  outlying  streamers 
may  be  resolved  with  a  good  3-inch  telescope. 
Sir  W.  Herschel  considered  that  the  number  of  the 
stars  composing  this  wonderful  object  was  at  least 
14,000.  The  accepted  views  respecting  nebulas 
would  place  this  and  other  clusters  far  beyond  the 
limits  of  our  sidereal  system,  and  would  make  the 
component  stars  not  very  unequal  (on  the  average) 
to  our  own  sun.  It  seems  to  me  far  more  probable, 
on  the  contrary,  that  the  cluster  belongs  to  our 
own  system,  and  that  its  components  are  very  much 
smaller  than  the  average  of  separate  stars.  Perhaps 
the  whole  mass  of  the  cluster  does  not  exceed  that 
of  an  average  first-magnitude  star. 

The  nebulae  92  M  and  50  $  may  be  found,  after 
a  little  searching,  from  the  positions  indicated  in 
the  map.  They  are  both  well  worthy  of  study, 
the  former  being  a  very  bright  globular  cluster,  the 
latter  a  bright  and  large  round  nebula.  The  spectra 
of  these,  as  of  the  great  cluster,  resemble  the  solar 
spectrum,  being  continuous,  though,  of  course,  very 
much  fainter. 


LYRA,  HERCULES,  CORVUS,  CRATER,  ETC.     53 

The  star  8  Herculis  (seen  at  the  bottom  of  the 
map)  is  a  wide  and  easy  double — a  beautiful  object. 
The  components,  situated  as  shown  in  Plate  3,  are 
of  the  fourth  and  eighth  magnitude,  and  coloured 
respectively  greenish-white  and  grape-red. 

The  star  K  Herculis  is  not  shown  in  the  map,  but 
may  be  very  readily  found,  lying  between  the  two 
gammas,  y  Herculis  and  y  Serpentis  (see  Frontis 
piece,  Map  2),  rather  nearer  the  latter.  It  is  a  wide 
double,  the  components  of  fifth  and  seventh  magni 
tude,  the  larger  yellowish-white,  the  smaller  ruddy 
yellow.* 

Kas  Algethi,  or  a  Herculis,  is  also  beyond  the 
limits  of  the  map,  but  may  be  easily  found  by  means 
of  Map  2,  Frontispiece.  It  is,  properly  speaking, 
a  multiple  star.  Considered  as  a  double,  the 
arrangement  of  the  components  is  that  shown  in 
Plate  3.  The  larger  is  of  magnitude  3.j,  the  smaller 
of  magnitude  5^ ;  the  former  orange,  the  latter 
emerald.  The  companion  stars  are  small,  and  re 
quire  a  good  telescope  to  be  well  seen.  Eas  Algethi 
is  a  variable,  changing  from  magnitude  3  to  magni 
tude  3J  in  a  period  of  6  6  A-  days. 

The  star  p  Herculis  is  a  closer  double.  The 
components  are  3"'7  apart,  and  situated  as  shown 
in  Plate  3.  The  larger  is  of  magnitude  4,  the 
smaller  5^ ;  the  former  bluish-white,  the  latter  pale 
emerald. 

There  are  other  objects  within  the  range  of  our 
map  which  are  well  worthy  of  study.  Such  are 
//,  Draconis,  a  beautiful  miniature  of  Castor  ;  y1  and 
•y2  Draconis,  a  wide  double,  the  distance  between  the 
components  being  nearly  62"  (both  grey)  ;  and  y1 

*  They  were  so  described  by  Admiral  Smyth  in  1839. 
Mr.  Main,  in  1862,  describes  them  as  straw-coloured  and 
reddish,  while  Mr.  Webb,  in  18G5,  saw  them  pale-yellovr 
and  lilac ! 


54  A    HALF-HOUR    WITH 

and  y2  Coronre,  a  naked-eye  double,  the  compo 
nents  being  6'  apart,  and  each  double  with  a  good 
3-inch  telescope. 

We  turn,  however,  to  another  region  of  the  sky. 
Low  down  towards  the  south  is  seen  the  small  con 
stellation  Corvus,  recognised  by  its  irregular  quadri 
lateral  of  stars.  Of  the  two  upper  stars,  the  left- 
hand  one  is  Algorab,  a  wide  double,  the  components 
placed  as  in  Plate  3,  23"*5  apart,  the  larger  of  mag 
nitude  8,  the  smaller  8J,  the  colours  pale  yellow 
and  purple. 

There  is  a  red  star  in  this  neighbourhood  which 
is  well  worth  looking  for.  To  the  right  of  Corvus 
is  the  constellation  Crater,  easily  recognised  as  form 
ing  a  tolerably  well-marked  small  group.  The  star 
Alkes,  or  a  Crateris,  must  first  be  found.  It  is  far 
from  being  the  brightest  star  in  the  constellation, 
and  may  be  assumed  to  have  diminished  consider 
ably  in  brilliancy  since  it  was  entitled  a  by  Bayer. 
It  will  easily  be  found,  however,  by  means  of  the 
observer's  star  maps.  If  now  the  telescope  be 
directed  to  Alkes,  there  will  be  found,  following 
him  at  a  distance  of  42'5  s,  and  about  one  minute 
southerly,  a  small  red  star,  R.  Crateris.  Like  most 
red  stars,  this  one  is  a  variable.  A  somewhat  smaller 
blue  star  may  be  seen  in  the  same  field. 

There  is  another  red  star  which  may  be  found 
pretty  easily  at  this  season.  First  find  the  stars 
77  and  o  Leonis,  the  former  forming  with  Ilegulus 
(now  lying  towards  the  south-west,  and  almost  ex 
actly  midway  between  the  zenith  and  the  horizon) 
the  handle  of  the  Sickle  in  Leo,  the  other  farther 
off  from  Eegulus  towards  the  right,  but  lower  down. 
Now  sweep  from  o  towards  77  with  a  low  power.* 
There  will  be  found  a  sixth-magnitude  star  about 

*  Or  the  observer  may  sweep  from  o  towards  v,  looking 
for  E  about  two-fifths  of  the  way  from  o  to  v. 


LYRA,  HERCULES,  CORVUS,  CRATER,  ETC.     55 

one-fourth  of  the  way  from  o  to  rj.  South,  following 
this,  will  be  found  a  group  of  four  stars,  of  which 
one  is  crimson.  This  is  the  star  R  Leonis.  Like 
K  Crateris  and  R  Leporis  it  is  variable. 

Next,  let  the  observer  turn  towards  the  south 
again.  Above  Corvus,  in  the  position  shown  in  the 
Frontispiece,  there  are  to  be  seen  five  stars,  forming 
a  sort  of  wide  V  with  somewhat  bowed  legs.  At 
the  angle  is  the  star  y  Virginis,  a  noted  double. 
In  1756  the  components  were  6^  seconds  apart. 
They  gradually  approached  till,  in  1836,  they  could 
not  be  separated  by  the  largest  telescopes.  Since 
then  they  have  been  separating,  and  they  are  now 
4^  seconds  apart,  situated  as  shown  in  Plate  3. 
They  are  nearly  equal  in  magnitude  (4),  and  both 
pale  yellow. 

The  star  y  Leonis  is  a  closer  and  more  beautiful 
double.  It  will  be  found  above  Regulus,  and  is  the 
brightest  star  on  the  blade  of  the  Sickle.  The  com 
ponents  are  separated  by  about  3  J-  seconds,  the  larger 
of  the  second,  the  smaller  of  the  fourth  magnitude  ; 
the  former  yellow-orange,  the  latter  greenish-yellow. 

Lastly,  the  star  i  Leonis  may  be  tried.  It  will 
be  a  pretty  severe  test  for  our  observer's  telescope, 
the  components  being  only  2"'4  apart,  and  the 
smaller  scarcely  exceeding  the  eighth  magnitude. 
The  brighter  (fourth  magnitude)  is  pale  yellow,  the 
other  light  blue. 


00  A    HALF-HOUR    WITH 


CHAPTER   IY. 

A  HALF-HOUR  WITH  BOOTES,  SCORPIO, 
OPHIUCHUS,  ETC. 

WE  now  commence  a  series  of  observations  suited 
to  the  third  quarter  of  the  year,  and  to  the  follow 
ing  hours  : — Ten  o'clock  on  the  22nd  of  July ;  nine 
on  the  8th  of  August ;  eight  on  the  23rd  of  August ; 
seven  on  the  8th  of  October;  and  intermediate 
hours  on  days  intermediate  to  these. 

We  look  first  for  the  Great  Bear  towards  the 
north-west,  and  thence  find  the  Pole-star.  Turning 
towards  the  north  we  see  Capella  and  ft  Aurigae  low 
down  and  slightly  towards  the  left  of  the  exact 
north  point.  The  Milky  Way  crosses  the  horizon 
towards  the  north-north-east  and  passes  to  the 
opposite  point  of  the  compass,  attaining  its  highest 
point  above  the  horizon  towards  east -south -east. 
This  part  of  the  Milky  Way  is  well  worth  observ 
ing,  being  marked  by  singular  variations  of  bril 
liancy.  Near  Arided  (the  principal  star  of  Cygnus, 
and  now  lying  due  east — some  twenty-five  degrees 
from  the  zenith)  there  is  seen  a  straight  dark  rift, 
and  near  this  space  is  another  larger  cavity,  which 
has  been  termed  the  northern  Coal-sack.  The 
space  between  y,  8,  and  ft  Cygni  is  covered  by  a 
large  oval  mass,  exceedingly  rich  and  brilliant. 
The  neighbouring  branch,  extending  from  e  Cygni, 
is  far  less  conspicuous  here,  but  near  Sagitta  be 
comes  brighter  than  the  other,  which  in  this  neigh 
bourhood  suddenly  loses  its  brilliancy  and  fading 
gradually  beyond  this  point  becomes  invisible  near 


PLATE  "LV. 


ff  A .  rrvchr,  <ltf  ff  AW 


BOOTES,    SCORPIO,    OPHIUCHUS,    ETC. 


57 


f3  Ophiuchi.  The  continuous  stream  becomes  patchy 
— in  parts  very  brilliant — where  it  crosses  Aquila 
and  Clypeus.  In  this  neighbourhood  the  other 
stream  reappears,  passing  over  a  region  very  rich 
in  stars.  We  see  now  the  greatest  extent  of  the 
Milky  Way,  towards  this  part  of  its  length,  ever 
visible  in  our  latitudes— just  as  in  spring  we  see 
its  greatest  extent  towards  Monoceros  and  Argo. 

I  may  note  here  in  passing  that  Sir  John  Her- 
schel's  delineation  of  the  northern  portion  of  the 
Milky  Way,  though  a  great  improvement  on  the 
views  given  in  former  works,  seems  to  require  revi 
sion,  and  especially  as  respects  the  very  remarkable 
patches  and  streaks  which  characterise  the  portion 
extending  over  Cepheus  and  Cygnus.  It  seems  to 
me,  also,  that  the  evidence  on  which  it  has  been 
urged  that  the  stars  composing  the  Milky  Way  are 
(on  an  average)  comparable  in  magnitude  to  our 
own  sun,  or  to  stars  of  the  leading  magnitudes,  is 
imperfect.  I  believe,  for  instance,  that  the  brilliant 
oval  of  milky  light  in  Cygnus  comes  from  stars 
intimately  associated  with  the  leading  stars  in  that 
constellation,  and  not  far  removed  in  space  (pro 
portionately)  beyond  them.  Of  course,  if  this  be 
the  case,  the  stars,  whose  combined  light  forms  the 
patch  of  milky  light,  must  be  far  smaller  than 
the  leading  brilliants  of  Cygnus.  However,  this 
is  not  the  place  to  enter  on  speculations  of  this 
sort ;  I  return  therefore  to  the  business  we  have 
more  immediately  in  hand. 

Towards  the  east  is  the  square  of  Pegasus  low 
down  towards  the  horizon.  Towards  the  south  is 
Scorpio,  distinguished  by  the  red  and  brilliant  An- 
tares,  and  by  a  train  of  conspicuous  stars.  Towards 
the  west  is  Bootes,  his  leading  brilliant — the  ruddy 
Arcturus — lying  somewhat  nearer  the  horizon  than 
the  zenith,  and  slightly  south  of  west.  Bootes  as 


58  A    HALF-HOUR    WITH 

a  constellation  is  easily  found  if  we  remember  that 
lie  is  delineated  as  chasing  away  the  Greater  Bear. 
Thus  at  present  he  is  seen  in  a  slightly  inclined 
position,  his  head  (marked  by  the  third-magnitude 
star  /3)  lying  due  west,  some  thirty  degrees  from  the 
zenith.  It  has  always  appeared  to  me,  by  the  way, 
that  Bootes  originally  had  nobler  proportions  than 
astronomers  now  assign  to  him.  It  is  known  that 
Canes  Venatici  now  occupy  the  place  of  an  up 
raised  arm  of  Bootes,  and  I  imagine  that  Corona 
Borealis,  though  undoubtedly  a  very  ancient  con 
stellation,  occupies  the  place  of  his  other  arm. 
Giving  to  the  constellation  the  extent  thus  implied, 
it  exhibits  (better  than  most  constellations)  the 
character  assigned  to  it.  One  can  readily  picture 
to  oneself  the  figure  of  a  Herdsman  with  upraised 
arms  driving  Ursa  Major  before  him.  This  view  is 
confirmed,  I  think,  by  the  fact  that  the  Arabs  called 
this  constellation  the  Vociferator. 

Bootes  contains  many  beautiful  objects.  Partly 
on  this  account,  and  partly  because  this  is  a  con 
stellation  with  which  the  observer  should  be  spe 
cially  familiar,  a  map  of  it  is  given  in  Plate  4. 

Arcturus  has  a  distant  pale  lilac  companion,  and 
is  in  other  respects  a  remarkable  and  interesting 
object.  It  is  of  a  ruddy  yellow  colour.  Schmidt, 
indeed,  considers  that  the  star  has  changed  colour 
of  late  years,  and  that  whereas  it  was  once  very  red 
it  is  now  a  yellow  star.  This  opinion  does  not 
seem  well  grounded,  however.  The  star  may  have 
been  more  ruddy  once  than  now,  though  no  other 
observer  has  noticed  such  a  peculiarity ;  but  it  is 
certainly  not  a  pure  yellow  star  at  present  (at  any 
rate  as  seen  in  our  latitude).  Owing  probably  to 
the  difference  of  colour  between  Vega,  Capella  and 
Arcturus,  photometricians  have  not  been  perfectly 
agreed  as  to  the  relative  brilliancy  of  these  objects. 


BOOTES,  SCORPIO,  OPHIUCHUS,  ETC.        59 

Some  consider  Vega  the  most  brilliant  star  in  the 
northern  heavens,  while  others  assign  the  supe 
riority  to  Capella.  The  majority,  however,  consider 
Arcturus  the  leading  northern  brilliant,  and  in  the 
whole  heavens  place  three  only  before  him,  viz., 
Sii'ius,  Canopus,  and  a  Centauri.  Arcturus  is  re 
markable  in  other  respects.  His  proper  motion  is 
very  considerable,  so  great  in  fact  that  since  the 
time  of  Ptolemy  the  southerly  motion  (alone)  of 
Arcturus  has  carried  him  over  a  space  nearly  half 
as  great  again  as  the  moon's  apparent  diameter. 
One  might  expect  that  so  brilliant  a  star,  apparently 
travelling  at  a  rate  so  great  compared  with  the 
average  proper  motions  of  the  stars,  must  be  com 
paratively  near  to  us.  This,  however,  has  not  been 
found  to  be  the  case.  Arcturus  is,  indeed,  one  of 
the  stars  whose  distance  it  has  been  found  possible 
to  estimate  roughly.  But  he  is  found  to  be  some 
three  ^  times  as  far  from  us  as  the  small  star  61 
Cygni,  and  more  than  seven  times  as  far  from  us 
as  a  Centauri. 

The  star  8  Bootis  is  a  wide  and  unequal  double, 
the  smaller  component  being  only  of  the  ninth 
magnitude. 

Above  Alkaid  the  last  star  in  the  tail  of  the 
Greater  Bear,  there  will  be  noticed  three  small 
stars.  These  are  0,  L,  and  K  Bootis,  and  are  usually 
placed  in  star-maps  near  the  upraised  hand  of  the 
Herdsman.  The  two  which  lie  next  to  Alkaid,  i  and 
K,  are  interesting  doubles.  The  former  is  a  wide 
double  (see  Plate  5),  the  magnitudes  of  components 
4  and  8,  their  colours  yellow  and  white.  The 
larger  star  of  this  pair  is  itself  double.  The  star  K 
Bootis  is  not  so  wide  a  double  (see  Plate  5),  the 
magnitudes  of  the  components  5  and  8,  their  colours 
white  and  faint  blue — a  beautiful  object. 

The  star  £  Bootis  is  an  exceedingly  interesting 


60  A    HA.LF-HOUK    WITH 

object.  It  is  double,  the  colours  of  the  components 
being  orange-yellow  and  ruddy  purple,  their  magni 
tudes  3Jr  and  6^.  When  this  star  was  first  observed 
by  Herschel  in  1780  the  position  of  the  components 
was  quite  different  from  that  presented  in  Plate  5. 
They  were  also  much  closer,  being  separated  by  a 
distance  of  less  than  3^  seconds.  Since  that  time 
the  smaller  component  has  traversed  nearly  a  full 
quadrant,  its  distance  from  its  primary  first  in 
creasing,  till  in  1831  the  stars  were  nearly  7^  se 
conds  apart,  and  thence  slowly  diminishing,  so  that 
at  present  the  stars  are  less  than  5  seconds  apart. 
The  period  usually  assigned  to  the  revolution  oi 
this  binary  system  is  117  years,  and  the  period  oi 
peri-astral  passage  is  said  to  be  1779.  It  appears  to 
me,  however,  that  the  period  should  be  about  108 
years,  the  epoch  of  last  peri-astral  passage  1777  and 
of  next  peri-astral  passage,  therefore,  1885.  The 
angular  motion  of  the  secondary  round  the  primary 
is  now  rapidly  increasing,  and  the  distance  between 
the  components  is  rapidly  diminishing,  so  that  in  a 
few  years  a  powerful  telescope  will  be  required  tc 
separate  the  pair. 

Not  far  from  £  is  TT  Bootis,  represented  in  Plate 
5  as  a  somewhat  closer  double,  but  in  reality — now 
at  any  rate — a  slightly  wider  pair,  since  the  distance 
between  the  components  of  £  has  greatly  diminished 
of  late.  Both  the  components  of  TT  are  white,  and 
their  magnitudes  arc  3J  and  6. 

We  shall  next  turn  to  an  exceedingly  beautiful 
and  delicate  object,  the  double  star  e  Bootis,  known 
also  as  JVIirac  and,  on  account  of  its  extreme  beauty, 
called  Pulcherrima  by  Admiral  Smyth.  The  corn- 
pi  »nents  of  this  beautiful  double  are  of  the  third 
and  seventh  magnitude,  the  primary  orange,  the 
secondary  sea-green.  The  distance  separating  the 
components- 'is  about  3  seconds,  perhaps  more;  it 


BOOTES,    SCORPIO,    OPHIUCHU8,    ETC.  61 

appears  to  have  been  slowly  increasing  during  the 
past  ten  or  twelve  years.  Smyth  assigns  to  this 
system  a  period  of  revolution  of  980  years,  but  there 
can  be  little  doubt  that  the  true  period  is  largely  in 
excess  of  this  estimate.  Observers  in  southern  lati 
tudes  consider  that  the  colours  of  the  components 
are  yellow  and  blue,  not  orange  and  green  as  most 
of  our  northern  observers  have  estimated  them. 

A  little  beyond  the  lower  left-hand  corner  of  the 
map  is  the  star  8  Serpentis,  in  the  position  shown 
in  the  Frontispiece,  Map  3.  This  is  the  star  which 
at  the  hour  and  season  depicted  in  Map  2  formed 
the  uppermost  of  a  vertical  row  of  stars,  which  has 
now  assumed  an  almost  horizontal  position.  The 
components  of  S  Serpentis  are  about  3J  seconds 
apart,  their  magnitudes  3  and  5,  both  white. 

The  stars  Ol  and  0*  Serpentis  form  a  wide  double, 
the  distance  between  the  components  being  21 J 
seconds.  They  are  nearly  equal  in  magnitude,  the 
primary  being  4^,  the  secondary  5.  Both  are 
yellow,  the  primary  being  of  a  paler  yellow  colour 
than  the  smaller  star.  But  the  observer  may  not 
know  where  to  look  for  0  Serpentis,  since  it  falls 
in  a  part  of  the  constellation  quite  separated  from 
that  part  in  which  8  Serpentis  lies.  In  fact  0  lies 
on  the  extreme  easterly  verge  of  the  eastern  half 
of  the  constellation.  It  is  to  be  looked  for  at  about 
the  same  elevation  as  the  brilliant  Altair,  and  (as  to 
azimuth)  about  midway  between  Altair  and  the  south. 

The  stars  a1  and  a2  Librae  form  a  wide  double, 
perhaps  just  separable  by  the  naked  eye  in  very 
favourable  weather.  The  larger  component  is  of 
the  third,  the  smaller  of  the  sixth  magnitude,  the 
former  yellow  the  latter  light  grey. 

The  star  ft  Libras  is  a  beautiful  light-green  star 
to  the  naked  eye;  in  the  telescope  a  wide  double, 
pale  emerald  and  light  blue. 


62  A    HALF  HOUR    WITH 

In  Scorpio  there  are  several  very  beautiful  ob 
jects  :— 

The  star  Antares  or  Cor  Scorpionis  is  one  of 
the  most  beautiful  of  the  red  stars.  It  has  been 
termed  the  Sirius  of  red  stars,  a  term  better  merited 
perhaps  by  Aldebaran,  save  for  this  that,  in  our 
latitude,  Antares  is,  like  Sirius,  always  seen  as  a 
brilliant  "  scintillator  "  (because  always  low  down), 
whereas  Aldebaran  rises  high  above  the  horizon. 
Antares  is  a  double  star,  its  companion  being  a 
minute  green  star.  In  southern  latitudes  the  com 
panion  of  Antares  may  be  seen  with  a  good  1-inch, 
but  in  our  latitudes  a  larger  opening  is  wanted. 
Mr.  Dawes  once  saw  the  companion  of  Antares 
shining  alone  for  seven  seconds,  the  primary  being 
hidden  by  the  moon.  He  found  that  the  colour  of 
the  secondary  is  not  merely  the  effect  of  contrast, 
but  that  this  small  star  is  really  a  green  sun. 

The  star  /3  Scorpionis  is  a  fine  double,  the  com 
ponents  13"'1  apart,  their  magnitudes  2  and  5r>, 
colours  white  and  lilac.  It  has  been  supposed  that 
this  pair  is  only  an  optical  double,  but  a  long 
time  must  elapse  before  a  decisive  opinion  can  be 
pronounced  on  such  a  point. 

The  star  a-  Scorpionis  is  a  wider  but  much  more 
difficult  double,  the  smaller  component  being  below 
the  9th  magnitude.  The  colour  of  the  primary  (4) 
is  white,  that  of  the  secondary  maroon. 

The  star  £  Scorpionis  is  a  neat  double,  the  com 
ponents  7"'  2  apart,  their  magnitudes  4^  and  7J, 
their  colours  white  and  grey.  This  star  is  really 
triple,  a  fifth-magnitude  star  lying  close  to  the 
primary. 

In  Ophiuchus,  a  constellation  covering  a  wide 
space  immediately  above  Scorpio,  there  are  several 
fine  doubles.  Among  others — 

39  Ophiuchi,  distance  between  components  12"*1, 


BOOTES,    SCORPIO,    OPHIUCHTTS,    ETC.  63 

their  magnitudes  5J  and  7^,  their  colours  orange 
and  blue. 

The  star  70  Ophiuchi,  a  fourth-magnitude  star  on 
the  right  shoulder  of  Ophiuchus,  is  a  noted  double. 
The  distance  between  the  components  about  5J", 
their  magnitudes  4J  and  7,  the  colours  yellow  and 
red.  The  pair  form  a  system  whose  period  of  re 
volution  is  about  95  years. 

36  Ophiuchi  (variable),  distance  5"'2,  magnitudes 
4J  and  6J,  colours  red  and  yellow. 

p  Opiuchi,  distance  4",  colours  yellow  and  blue, 
magnitudes  5  and  7. 

Between  a  and  /?  Scorpionis  the  fine  nebula  80  M 
may  be  looked  for.  (Or  more  closely  thus : — below 
ft  is  the  wide  double  to1  and  to2  Scorpionis ;  about  as 
far  to  the  right  of  Antares  is  the  star  cr  Scorpionis, 
and  immediately  above  this  is  the  fifth-magnitude 
star  19.)  The  nebula  we  seek  lies  between  19  and  w, 
nearer  to  19  (about  two-fifths  of  the  way  towards  to). 
This  nebula  is  described  by  Sir  W.  Herschel  as 
"the  richest  and  most  condensed  mass  of  stars 
which  the  firmament  offers  to  the  contemplation  of 
astronomers." 

There  are  two  other  objects  conveniently  situated 
for  observation,  which  the  observer  may  now  turn 
to.  The  first  is  the  great  cluster  in  the  sword- 
hand  of  Perseus  (see  Plate  4),  now  lying  about 
28°  above  the  horizon  between  N.E.  and  N.N.E. 
The  stars  y  and  S  Cassiopeia  (see  Map  3  of 
Frontispiece)  point  towards  this  cluster,  which 
is  rather  farther  from  8  than  8  from  y,  and  a  little 
south  of  the  produced  line  from  these  stars.  The 
cluster  is  well  seen  with  the  naked  eye,  even  in 
nearly  full  moonlight.  In  a  telescope  of  moderate 
power  this  cluster  is  a  magnificent  object,  and,  tio 
telescope  has  yet  revealed  its  full  glory.  The 
view  in  Plate  5  gives  but  the  faintest  conception 


64  A    HALF-HOUK    WITH 

of  the  glories  of  x  PerseL  Sir  W.  Herschel  tried 
in  vain  to  gauge  the  depths  of  this  cluster  with  his 
most  powerful  telescope.  He  spoke  of  the  most 
distant  parts  as  sending  light  to  us  which  must 
have  started  4000  or  5000  years  ago.  But  it 
appears  improbable  that  the  cluster  has  in  reality 
so  enormous  a  longitudinal  extension  compared  with 
its  transverse  section  as  this  view  would  imply. 
On  the  contrary,  I  think  we  may  gather  from  the 
appearance  of  this  cluster,  that  stars  are  far  less 
uniform  in  size  than  has  been  commonly  supposed, 
and  that  the  mere  irresolvability  of  a  cluster  is 
no  proof  of  excessive  distance.  It  is  unlikely  that 
the  faintest  component  of  the  cluster  is  farther 
off  than  the  brightest  (a  seventh-magnitude  star) 
in  the  proportion  of  more  than  about  20  to  19,  while 
the  ordinary  estimate  of  star  magnitudes,  applied 
by  Herschel,  gave  a  proportion  of  20  or  30  to  1  at 
least.  I  can  no  more  believe  that  the  components 
of  this  cluster  are  stars  greatly  varying  in  distance, 
but  accidentally  seen  in  nearly  the  same  direction, 
(or  that  they  form  an  enormously  long  system  turned 
by  accident  directly  towards  the  earth),  than  I 
could  look  on  the  association  of  several  thousand 
persons  in  the  form  of  a  procession  as  a  fortuitous 
arrangement. 

Next  there  is  the  great  nebula  in  Andromeda — 
known  as  "  the  transcendantly  beautiful  queen  of 
the  nebulae."  It  will  not  be  difficult  to  find  this 
object.  The  stars  e  and  8  Cassiopeiae  (Map  3, 
Frontispiece)  point  to  the  star  j3  Andromedae.  Al 
most  in  a  vertical  line  above  this  star  are  two 
fourth-magnitude  stars  /x  and  y,  and  close  above  vy 
a  little  to  the  right,  is  the  object  we  seek — visible 
to  the  naked  eye  as  a  faint  misty  spot.  To  tell 
the  truth,  the  transcendantly  beautiful  queen  of  the 
nebulae  is  rather  a  disappointing  object  in  an  ordi- 


BOOTES,    SCORPIO,    OPHIUCHUS,    ETC.  65 

nary  telescope.  There  is  seen  a  long  oval  or  len 
ticular  spot  of  light,  very  bright  near  the  centre, 
especially  with  low  powers.  But  there  is  a  want  of 
the  interest  attaching  to  the  strange  figure  of  the 
Great  Orion  nebula.  The  Andromeda  nebula  has 
been  partially  resolved  by  Lord  Eosse's  great  re 
flector,  and  (it  is  said)  more  satisfactorily  by  the 
great  refractor  of  Harvard  College.  In  the  spec 
troscope,  Mr.  Huggins  informs  us,  the  spectrum  is 
peculiar.  Continuous  from  the  blue  to  the  orange, 
the  light  there  "  appears  to  cease  very  abruptly ; " 
there  is  no  indication  of  gaseity. 

Lastly,  the  observer  may  turn  to  the  pair  Mizar 
and  Alcor,  the  former  the  middle  star  in  the  Great 
Bear's  tail,  the  latter  15'  off.  It  seems  quite  clear, 
by  the  way,  that  Alcor  has  increased  in  brilliancy 
of  late,  since  among  the  Arabians  it  was  considered 
an  evidence  of  very  good  eyesight  to  detect  Alcor, 
whereas  this  star  may  now  be  easily  seen  even  in 
nearly  full  moonlight.  Mizar  is  a  double  star, 
and  a  fourth  star  is  seen  in  the  same  field  of 
view  with  the  others  (see  Plate  5).  The  distance 
between  Mizar  and  its  companion  is  14"-4;  the 
magnitude  of  Mizar  3,  of  the  companion  5 ;  'their 
colours  white  and  pale  green,  respectively. 


66  A    HALF-HOUK    WITH 


CHAPTEK  V. 


A  HALF-HOUK  WITH  ANDROMEDA,  CYGNUS,  ETC, 

OUR  last  half-hour  with  the  double  stars,  &c.,  must 
be  a  short  one,  as  we  have  already  nearly  filled  the 
space  allotted  to  these  objects.  The  observations 
now  to  be  made  are  supposed  to  take  place  during 
the  fourth  quarter  of  the  year, — at  ten  o'clock  on 
October  23rd;  or  at  nine  on  November  7th;  or 
at  eight  on  November  22nd ;  or  at  seven  on 
December  6th ;  or  at  hours  intermediate  to  these 
on  intermediate  days. 

We  look  first,  as  in  former  cases,  for  the  Great 
Bear,  now  lying  low  down  towards  the  north. 
Towards  the  north-east,  a  few  degrees  easterly,  are 
the  twin-stars  Castor  and  Pollux,  in  a  vertical  posi 
tion,  Castor  uppermost.  Above  these,  a  little  towards 
the  right,  we  see  the  brilliant  Capella ;  and  between 
Capella  and  the  zenith  is  seen  the  festoon  of  Per 
seus.  Cassiopeia  lies  near  the  zenith,  towards  the 
north,  and  tho  Milky  Way  extends  from  the  eastern 
horizon  across  the  zenith  to  the  western  horizon. 
Low  down  in  the  east  is  Orion,. half  risen  above  the 
horizon.  Turning  to  the  south,  we  see  high  up 
above  the  horizon  the  square  of  Pegasus.  Low 
down  towards  the  south-south-west  is  Fomalhaut, 
pointed  to  by  ft  and  a  Pegasi.  Towards  the  west, 
about  half-way  between  the  zenith  and  the  horizon, 
is  the  noble  cross  in  Cygnus ;  below  which,  towards 
the  left,  we  see  Altair,  n-nd  his  companions  ft  and 
y  AquilfB :  while  towards  the  right  we  see  the 
brilliant  Vega. 

During  this  half-hour  we  shall  not  confine  our- 


PLATE 


i-  Boolis  tf.liootis  Oai«  tkroli.  £>  Bootis 


H  Scorpii  (.',     i>oo»'pit  70  Ophiudii          ?  Opniudu  <i  Stn-porit 


y Andromeda.          o/Pisciuni  &  F.quu^ei 


'"  axid  ,    i^i  iixorns 


ANDROMEDA,    CYGNUS,    ETC.  67 

selves  to  any  particular  region  of  the  heavens,  but 
sweep  the  most  conveniently  situated  constellations. 

First,  however,  we  should  recommend  the  observer 
to  try  and  get  a  good  view  of  the  great  nebula  in 
Andromeda,  which  is  not  conveniently  situated  for 
observation,  but  is  so  high  that  after  a  little  trouble 
the  observer  may  expect  a  more  distinct  view  than 
in  the  previous  quarter.  He  will  see  fi  Andromeda 
towards  the  south-east,  about  18°  from  the  zenith, 
fj.  and  v  nearly  in  a  line  towards  the  zenith,  and  the 
nebula  about  half-way  between  /?  and  the  zenith. 

With  a  similar  object  it  will  be  well  to  take 
another  view  of  the  great  cluster  in  Perseus,  about 
18°  from  the  zenith  towards  the  east-north-east  (see 
the  pointers  y  and  8  Cassiopeiae  in  Map  4,  Frontis 
piece),  the  cluster  being  between  8  Cassiopeia  and 
a  Persei. 

Not  very  far  off  is  the  wonderful  variable  Algol, 
now  due  east,  and  about  58°  above  the  horizon. 
The  variability  of  this  celebrated  object  was  doubt 
less  discovered  in  very  ancient  times,  since  the  name 
Al-gol,  or  "  the  Demon"  seems  to  point  to  a  know 
ledge  of  the  peculiarity  of  this  "slowly  winking 
eye."  To  Goodricke,  however,  is  due  the  rediscovery 
of  Algol's  variability.  The  period  of  variation  is 
2  d.  20  h.  48  m. ;  during  2  h.  14  m.  Algol  appears  of 
the  second  magnitude ;  the  remaining  6  J  hours  are 
occupied  by  the  gradual  decline  of  the  star  to  the 
fourth  magnitude,  and  its  equally  gradual  return  to 
the  second.  It  will  be  found  easy  to  watch  the  vari 
ations  of  this  singular  object,  though,  of  course, 
many  of  the  minima  are  attained  in  the  daytinx 
The  following  may  help  the  observer  : — 

On  October  8th,  1867,  at  about  half-past  eleve. 
in  the  evening,  I  noticed  that  Algol  had  reached  its 
minimum  of  brilliancy.  Hence  the  next  minimum 
was  attained  at  about  a  quarter-past  eight  on  tK. 
evening  of  October  llth;  the  next  at  about  five  on 

F  2 


68 


A    HALF-HOUK    WITH 


the  evening  of  October  14th,  and  so  on.  Now,  if 
this  process  be  carried  on,  it  will  be  found  that  the 
next  evening  minimum  occurred  at  about  10  h. 
(circiter}  on  the  evening  of  October  31st,  the  next  at 
about  llh.  30m.  on  the  evening  of  November  20th. 
Thus  at  whatever  hour  any  minimum  occurs,  another 
occurs  six  weeks  and  a  day  later,  at  about  the  same 
hour.  This  would  be  exact  enough  if  the  period  of 
variation  were  exactly  2  d.  20  m.  48  s.,  but  the  period 
is  nearly  a  minute  greater,  and  as  there  are  fifteen 
periods  in  six  weeks  and  a  day,  it  results  that  there 
is  a  difference  of  about  13  m.  in  the  time  at  which 
the  successive  recurrences  at  nearly  the  same  hour 
take  place.  Hence  we  are  able  to  draw  up  the  two 
following  Tables,  which  will  suffice  to  give  all  the 
minima  conveniently  observable  during  the  next  two 
years.  Starting  from  a  minimum  at  about  llh.  45  m. 
on  November  20th,  1867,  and  noticing  that  the  next 
43-day  period  (with  the  13  m.  added)  gives  us  an 
observation  at  midnight  on  January  2nd,  1868,  and 
that  successive  periods  would  make  the  hour  later 
yet,  we  take  the  minimum  next  after  that  of 
January  2nd,  viz.  that  of  January  5th,  1868, 
8  h.  48  m.,  and  taking  43-day  periods  (with  13  m. 
added  to  each),  we  get  the  series — 


Jan.   5,  1868 

h.   m. 
8  45  P.M. 

Mar.  10,  1869 

TV/for  1  S 

h.   m. 
10  25P.M. 

7  4'5   * 

A  nr  oc 

7  56 

o    q 

May  16,  
June  25,  

9  37  - 

9^0 

July  20,  

Spnt  1 

8  22  — 
3  35 

Aug.   /, 
Sept.  19,  
Nov.   1,  
Dec.  14,  — 
Jan.  26,  1869 

10   3  — 
10  16  — 

10  29  — 
10  42  — 

Oct.  14,  
Nov.  26,  
Jan.  8,  1870 
Feb.  20,  

8  48  — 
9   1  — 
9  14  - 

9  27  — 

*  Here  a  single  peiiod  only  is  taken,  to  get  back  to  a  con 
venient  hour  of  the  evening. 


ANDROMEDA,    CYGNUS,    ETC. 


69 


From  the  minimum  at  about  10  P.M.  on  October 
31st,  1867,  we  get  in  like  manner  the  series — 


Dec.  13,  1867 
Jan.  25,  1868 
Mar.   8,  
Apr.  20,  - 
June   2,  
June   5,  
July  18,  

h.   m. 
10  18p.M. 
10  26  — 
10  39  — 
10  52  — 
11   5  — 
7  53  —  * 
y   (3  

Jan.  6,  1869 
Feb.  18,  
Apr.  2,  
May  15,  
June  27,  
Aug.  9,  

Sent  91 

h.   m. 
8  58  P.M. 
9  11  — 
9  24  — 
9  37  — 
9  50  — 
10   3  — 
in  in 

Aug.  30,  
Oct.  12,  

Nov.  24,  

8   19  — 
8  32  — 
8  45  — 

Xov.  3,  
Dec.  16,  
Jan.  28,  1870 

10  29  — 
10  42  — 
10  55  — 

From  one  or  other  of  these  tables  every  observ 
able  minimum  can  be  obtained.  Thus,  suppose  the 
observer  wants  to  look  for  a  minimum  during  the 
last  fortnight  in  August,  1868.  The  first  table 
gives  him  no  information,  the  latter  gives  him  a 
minimum  at  8  h.  19  m.  P.M.  on  August  30 ;  hence 
of  course  there  is  a  minimum  at  11  h.  31  m.  P.M.  on 
August  27 ;  and  there  are  no  other  conveniently 
observable  minima  during  the  fortnight  in  question. 

The  cause  of  the  remarkable  variation  in  this 
star's  brilliancy  has  been  assigned  by  some  astro 
nomers  to  the  presence  of  an  opaque  secondary, 
which  transits  Algol  at  regular  intervals;  others 
have  adopted  the  view  that  Algol  is  a  luminous 
secondary,  revolving  around  an  opaque  primary. 
Of  these  views  the  former  seems  the  most  natural 
and  satisfactory.  It  points  to  a  secondary  whose 
mass  bears  a  far  greater  proportion  to  that  of  the 
primary,  than  the  mass  ev.en  of  Jupiter  bears  to  the 
sun ;  the  shortness  of  the  period  is  also  remarkable. 
It  may  be  noticed  that  observation  points  to  a 
gradual  diminution  in  the  period  of  Algol's  varia- 

*  Here  a  single  period  only  is  taken,  to  get  back  to  a  con 
venient  hour  of  the  evening. 


70  A   HALF-HOUR    WITH 

tion,  and  the  diminution  seems  to  be  proceeding 
more  and  more  rapidly.  Hence  (assuming  the 
existence  of  a  dark  secondary)  we  must  suppose  that 
either  it  travels  in  a  resisting  medium  which  is 
gradually  destroying  its  motion,  or  that  there  are 
other  dependent  orbs  whose  attractions  affect  the 
period  of  this  secondary.  In  the  latter  case  the 
decrease  in  the  period  will  attain  a  limit  and  be 
followed  by  an  increase. 

However,  interesting  as  the  subject  may  be,  it  is 
a  digression  from  telescopic  work,  to  which  we  now 
return. 

Within  the  confines  of  the  second  map  in  Plate 
4  is  seen  the  fine  star  y  Andromedas.  At  the 
hour  of  our  observations  it  lies  high  up  towards 
E.S.E.  It  is  seen  as  a  double  star  with  very  mode 
rate  telescopic  power,  the  distance  between  the  com 
ponents  being  upwards  of  10"  ;  their  magnitudes  3 
and  5^,  their  colours  orange  and  green.  Perhaps 
there  is  no  more  interesting  double  visible  with  low 
powers.  The  smaller  star  is  again  double  in  first- 
class  telescopes,  the  components  being  yellow  and 
blue  according  to  some  observers,  but  according  to 
others,  both  green. 

Below  y  AndromedaB  lie  the  stars  (3  and  y  Tri- 
angulorum,  y  a  fine  naked-eye  triple  (the  compa 
nions  being  8  and  77  Triangulorum),  a  fine  object 
with  a  very  low  power.  To  the  right  is  a  Trian 
gulorum,  certainly  less  brilliant  than  /3.  Below  a 
are  the  three  stars  a,  /3,  and  y  Arietis,  the  first  an 
unequal  and  difficult  double,  the  companion  being 
purple,  and  only  just  visible  (under  favourable  cir 
cumstances)  with  a  good  3-inch  telescope ;  the  last 
an  easy  double,  interesting  as  being  the  first  ever 
discovered  (by  Hook,  in  1664),  the  colours  of  com 
ponents  white  and  grey. 

Immediately  below  a  Arietis  is  the  star  a  Ceti, 


ANDROMEDA,    CYGNUS,    ETC.  71 

towards  the  right  of  which  (a  little  lower)  is  Mira, 
a  wonderful  variable.  This  star  has  a  period  of 
331-g-  days;  during  a  fortnight  it  appears  as  a  star 
of  the  2nd  magnitude, — on  each  side  of  this  fortnight 
there  is  a  period  of  three  months  during  one  of 
which  the  star  is  increasing,  while  during  the  other 
it  is  diminishing  in  brightness  :  during  the  remain 
ing  five  months  of  the  period  the  star  is  invisible 
to  the  naked  eye.  There  are  many  peculiarities 
and  changes  in  the  variation  of  this  star,  into  which 
space  will  not  permit  me  to  enter. 

Immediately  above  Mira  is  the  star  a  Piscium  at 
the  knot  of  the  Fishes'  connecting  band.  This  is  a 
fine  double,  the  distance  between  the  components 
being  about  3^",  their  magnitudes  5  and  6,  their 
colours  pale  green  and  blue  (see  Plate  5). 

Close  to  y  Aquarii  (see  Frontispiece,  Map  4), 
above  and  to  the  left  of  it,  is  the  interesting  double 
£  Aquarii ;  the  distance  between  the  components  is 
about  3.V,  their  magnitudes  4  and  4.V,  both  whitish 
yellow.  The  period  of  this  binary  seems  to  be 
about  750  years. 

Turning  next  towards  the  south-west  we  see  the 
second-magnitude  star  e  Pegasi,  some  40°  above  the 
horizon.  This  star  is  a  wide  but  not  easy  double, 
the  secondary  being  only  of  the  ninth  magnitude ;  its 
colour  is  lilac,  that  of  the  primary  being  yellow. 

Towards  the  right  of  e  Pegasi  and  lower  down 
are  seen  the  three  fourth-magnitude  stars  which  mark 
the  constellation  Equuleus.  Of  these  the  lowest  is 
a,  to  the  right  of  which  lies  e  Equulei,  a  fifth-magni 
tude  star,  really  triple,  but  seen  as  a  double  star 
with  ordinary  telescopes  (Plate  5).  The  distance 
between  the  components  is  nearly  11",  their  colours 
white  and  blue,  their  magnitudes  5^  and  7^-.  The 
primary  is  a  very  close  double,  which  appears,  how 
ever,  to  be  opening  out  rather  rapidly. 

Immediately  below  Equuleus  are  the  stars  a1  and 


72  A   HALF-IXOUK   WITH 

of  Capricorn!,  seen  as  a  naked-eye  double  to  the 
right  of  and  above  {$.  Both  a1  and  a2  are  yellow ; 
a2  is  of  the  3rd,  a1  of  the  4th  magnitude  ;  in  a  good 
telescope  five  stars  are  seen,  the  other  three  being 
blue,  ash-coloured,  and  lilac.  The  star  /3  Capri- 
corni  is  also  a  wide  double,  the  components  yellow 
and  blue,  with  many  telescopic  companions. 

To  the  right  of  Equuleus,  towards  the  west-south 
west  is  the  constellation  Delphinus.  The  upper 
left-hand  star  of  the  rhombus  of  stars  forming  the 
head  of  the  Delphinus  is  the  star  y  Delphini,  a 
rather  easy  double  (see  Plate  5),  the  components 
being  nearly  1 2"  apart,  their  magnitudes  4  and  7, 
their  colours  golden  yellow  and  flushed  grey. 

Turn  we  next  to  the  charming  double  Albireo,  on 
the  beak  of  Cygnus,  about  36°  above  the  horizon 
towards  the  west.  The  components  are  34 ^"  apart, 
their  magnitudes  3  and  6,  their  colours  orange- 
yellow,  and  blue.  It  has  been  supposed  (perhaps 
on  insufficient  evidence)  that  this  star  is  merely  an 
optical  double.  It  must  always  be  remembered 
that  a  certain  proportion  of  stars  (amongst  those 
separated  by  so  considerable  a  distance)  must  be 
optically  combined  only. 

The  star  ^  Cygni  is  a  wide  double  (variable)  star. 
The  components  are  separated  by  nearly  26",  their 
magnitudes  5  and  9,  their  colours  yellow  and  light 
blue,  x  may  be  found  by  noticing  that  there  is  a 
cluster  of  small  stars  in  the  middle  of  the  triangle 
formed  by  the  stars  y,  S,  and  ft  Cygni  (see  Map  4, 
Frontispiece),  and  that  x  is  the  nearest  star  of  the 
clust&r  to  (3.  The  star  <£  Cygni,  which  is  just  above 
and  very  close  to  ft  (Albireo),  does  not  belong  to 
the  cluster,  x  ig  about  half  as  far  again  from  </>  as 
<£  from  Albireo.  But  as  ^  descends  to  the  llth 
magnitude  at  its  minimum  the  observer  must  not 
always  expect  to  find  it  very  easily.  It  has  been 
known  to  be  invisible  at  the  epoch  when  it  should 


ANDROMEDA,    CYGNUS,    ETC.  73 

have  been  most  conspicuous.     The  period  of  this 
variable  is  406  days. 

The  star  61  Cygni  is  an  interesting  one.  So  far 
as  observation  has  yet  extended,  it  would  seem  to  be 
the  nearest  to  us  of  all  stars  visible  in  the  northern 
hemisphere.  It  is  a  fine  double,  the  components 
nearly  equal  (5  J-  and  6),  both  yellow,  and  nearly 
19"  apart.  The  period  of  this  binary  appears  to  be 
about  540  years.  To  find  61  Cygni  note  that  e  and 
8  Cygni  form  the  diameter  of  a  semicircle  divided 
into  two  quadrants  by  a  Cygni  (Arided).  On  this 
semicircle,  on  either  side  of  a,  lie  the  stars  v  and 
a  Cygni,  v  towards  e.  Now  a  line  from  a  to  v  pro 
duced  passes  very  near  to  61  Cygni  at  a  distance 
from  v  somewhat  greater  than  half  the  distance  of  v 
from  a. 

The  star  //,  Cygni  lies  in  a  corner  of  the  constel 
lation,  rather  farther  from  £  than  £  from  e  Cygni. 
A  line  from  e  to  £  produced  meets  K  Pegasi,  a  fourth- 
magnitude  star ;  and  //,  Cygni,  a  fifth-magnitude  star, 
lies  close  above  K  Pegasi.  The  distance  between 
the  components  is  about  5J",  their  magnitudes  5 
and  6,  their  colours  white  and  pale  blue. 

The  star  i/r  Cygni  may  next  be  looked  for,  but  for 
this  a  good  map  of  Cygnus  will  be  wanted,  as  «/r  is 
not  pointed  to  by  any  well-marked  stars.  A  line 
from  a,  parallel  to  the  line  joining  y  and  8,  and 
about  one-third  longer  than  that  line,  would  about 
mark  the  position  of  \f/  Cygni.  The  distance  between 
the  components  of  this  double  is  about  3J",  their 
magnitudes  5^  and  8,  their  colours  white  and  lilac. 

Lastly,  the  observer  may  turn  to  the  stars  yx  and 
y2  Draconis  towards  the  north-west  about  40°  above 
the  horizon  (they  are  included  in  the  second  map 
of  Plate  2).  They  form  a  wide  double,  having 
equal  (fifth-magnitude)  components,  both  grey.  (See 
Jrlate  o.j 


74:  HALF-HOURS   WITH    THE    PLANETS. 


CHAPTEE  VI. 


HALF-HOUES  WITH  THE  PLANETS. 

IN  observing  the  stars,  we  can  select  a  part  of  the 
heavens  which  may  be  conveniently  observed ;  and  in 
this  way  in  the  course  of  a  year  we  can  observe 
every  part  of  the  heavens  visible  in  our  northern 
hemisphere.  But  with  the  planets  the  case  is  not 
quite  so  simple.  They  come  into  view  at  no  fixed 
season  of  the  year  :  some  of  them  can  never  be  seen 
%  night  on  the  meridian ;  and  they  all  shift  their 
place  among  the  stars,  so  that  we  require  some 
method  of  determining  where  to  look  for  them  on 
any  particular  night,  and  of  recognising  them  from 
neighbouring  fixed  stars. 

The  regular  observer  will  of  course  make  use  of  the 
'Nautical  Almanac';  but  '  Dietrichsen  and  Hannay's 
Almanac '  will  serve  every  purpose  of  the  amateur 
telescopist.  I  will  briefly  describe  those  parts  of 
the  almanac  which  are  useful  to  the  observer. 

It  will  be  found  that  three  pages  are  assigned  to 
each  month,  each  page  giving  different  information. 
If  we  call  these  pages  I.  II.  III.,  then  in  order  that 
page  I.  for  each  month  may  fall  to  the  left  of  the 
open  double  page,  and  also  that  I.  and  II.  may  be 
open  together,  the  pages  are  arranged  in  the  follow 
ing  order  :  I.  II.  III.;  III.  I.  II.;  I.  II.  III.;  and 
so  on. 

Now  page  III.  for  any  month  does  not  concern 
the  amateur  observer.  It  gives  information  con 
cerning  the  moon's  motions,  which  is  valuable  to  the 
sailor,  and  interesting  to  the  student  of  astronomy, 
but  not  applicable  to  amateur  observation. 


PLATE   VI 


Mars.     .Summer      of      tta     SoutWu       Hemisp 


Mztrs .      *Sumtii«>i         of      tlv      Northern       HeinispJtie 


HALF-HOUKS    WITH    THE    PLANETS.  75 

We  have  then  only  pages  I.  and  II.  to  consider  : — 
Across  the  top  of  both  pages  the  right  ascension 
and  declination  of  the  planets  Venus,  Jupiter,  Mars, 
Saturn,  Mercury,  and  Uranus  are  given,  accompanied 
by  those  of  two  conspicuous  stars.  This  information 
is  very  valuable  to  the  telescopist.  In  the  first  place, 
as  we  shall  presently  see,  it  shows  him  what  planets 
are  well  situated  for  observation,  and  secondly  it 
enables  him  to  map  down  the  path  of  any  planet 
from  day  to  day  among  the  fixed  stars.  This  is  a 
very  useful  exercise,  by  the  way,  and  also  a  very 
instructive  one.  The  student  may  either  make  use 
of  the  regular  maps  and  mark  down  the  planet's  path 
in  pencil,  taking  a  light  curve  through  the  points 
given  by  the  data  in  his  almanac,  or  he  may  lay 
down  a  set  of  meridians  suited  to  the  part  of  the 
heavens  traversed  by  the  planet,  and  then  proceed 
to  mark  in  the  planet's  path  and  the  stars,  taking 
the  latter  either  from  his  maps  or  from  a  con 
venient  list  of  stars.*  My  '  Handbook  of  the  Stars  ' 
has  been  constructed  to  aid  the  student  in  these 
processes.  It  must  be  noticed  that  old  maps  are  not 
suited  for  the  work,  because,  through  precession,  the 
stars  are  all  out  of  place  as  respects  K.  A.  and  Dec. 
Even  the  Society's  maps,  constructed  so  as  to  be 
right  for  1830,  are  beginning  to  be  out  of  date.  But 
a  matter  of  20  or  30  years  either  way  is  not  im 
portant.!  My  Maps,  Handbook  and  Zodiac-chart 
have  been  constructed  for  the  year  1880,  so  as  to  be 
serviceable  for  the  next  fifty  years  or  so. 

*  I  have  constructed  a  zodiac-chart,  which  will  enable  the 
student  to  mark  in  the  path  of  a  planet,  at  any  season  of  the 
year,  from  the  recorded  places  in  the  almanacs. 

t  It  is  convenient  to  remember  that  through  precession  a 
star  near  the  ecliptic  shifts  as  respects  the  R.  A.  and  Dec. 
lines,^  through  an  arc  of  one  degree  — or  nearly  twice  the 
moon's  diameter— in  about  72  years,  all  other  stars  through 
a  less  arc. 


76  HALF-HOURS   WITH    THE   PLANETS. 

Next,  below  the  table  of  tlie  planets,  we  have  a  set 
of  vertical  columns.  These  are,  in  order,  the  days 
of  the  month,  the  calendar — in  which  are  included 
some  astronomical  notices,  amongst  others  the  dia 
meter  of  Saturn  on  different  dates,  the  hours  at  which 
the  sun  rises  and  sets,  the  sun's  right  ascension, 
declination,  diameter,  and  longitude;  then  eight 
columns  which  do  not  concern  the  observer;  after 
which  come  the  hours  at  which  the  moon  rises  and 
sets,  the  moon's  age ;  and  lastly  (so  far  as  the  ob 
server  is  concerned)  an  important  column  about 
Jupiter's  system  of  satellites. 

Next,  we  have,  at  the  foot  of  the  first  page,  the 
hours  at  which  the  planets  rise,  south,  and  set ;  and 
at  the  foot  of  the  second  page  we  have  the  dates 
of  conjunctions,  oppositions,  and  of  other  phenomena, 
the  diameters  of  Venus,  Jupiter,  Mars,  and  Mercury, 
and  finally  a  few  words  respecting  the  visibility  of 
these  four  planets. 

After  the  thirty-six  pages  assigned  to  the  months 
follow  four  (pp.  42-46)  in  which  much  important 
astronomical  information  is  contained ;  but  the  points 
which  most  concern  our  observer  are  (i.)  a  small 
table  showing  the  appearance  of  Saturn's  rings,  and 
(ii.)  a  table  giving  the  hours  at  which  Jupiter's 
satellites  are  occulted  or  eclipsed,  re-appear,  &c. 

We  will  now  take  the  planets  in  the  order  of  their 
distance  from  the  sun :  we  shall  see  that  the  infor 
mation  given  by  the  almanac  is  very  important  to 
the  observer. 

Mercury  is  so  close  to  the  sun  as  to  be  rarely  seen 
with  the  naked  eye,  since  he  never  sets  much  more 
than  two  hours  and  a  few  minutes  after  the  sun,  or 
rises  by  more  than  that  interval  before  the  sun.  It 
must  not  be  supposed  that  at  each  successive  epoch 
of  most  favourable  appearance  Mercury  sets  so  long 
after  the  sun  or  rises  so  long  before  him.  It  would 


HALF-HOURS   WITU    THE    PLANETS.  77 

occupy  too  much  of  our  space  to  enter  into  the  circum 
stances  which  affect  the  length  of  these  intervals. 
The  question,  in  fact,  is  not  a  very  simple  one.  All 
the  necessary  information  is  given  in  the  almanac. 
We  merely  notice  that  the  planet  is  most  favourably 
seen  as  an  evening  star  in  spring,  and  as  a  morning 
star  in  autumn.* 

The  observer  with  an  equatorial  has  of  course  no 
difficulty  in  finding  Mercury,  since  he  can  at  once 
direct  his  telescope  to  the  proper  point  of  the 
heavens.  But  the  observer  with  an  alt-azimuth 
might  fail  for  years  together  in  obtaining  a  sight  of 
this  interesting  planet,  if  he  trusted  to  unaided  naked- 
eye  observations  in  looking  for  him.  Copernicus 
never  saw  Mercury,  though  he  often  looked  for  him ; 
and  Mr.  Hind  tells  me  he  has  seen  the  planet  but 
once  with  the  naked  eye — though  this  perhaps  is  not 
a  very  remarkable  circumstance,  since  the  systematic 
worker  in  an  observatory  seldom  has  occasion  to  ob 
serve  objects  with  the  unaided  eye. 

By  the  following  method  the  observer  can  easily 
pick  up  the  planet. 

Across  two  uprights  (Fig.  10)  nail  a  straight 
rod,  so  that  when  looked  at  from  some  fixed  point  of 
view  the  rod  may  correspond  to  the  sun's  path  near  the 
time  of  observation.  The  rod  should  be  at  right- 
angles  to  the  line  of  sight  to  its  centre.  Fasten 
another  rod  at  right  angles  to  the  first.  From  the 
point  at  which  the  rods  cross  measure  off  and  mark 

*  Mercury  is  best  seen  when  in  quadrature  to  the  sun,  but 
not  (as  I  have  seen  stated)  at  those  quadratures  in  which  he 
attains  his  maximum  elongation  from  the  sun.  This  will 
appear  singular,  because  the  maximum  elongation  is  about 
27°,  the  minimum  only  about  18°.  But  it  happens  that 
in  our  northern  latitudes  Mercury  is  always  south  of  the  sun 
when  he  attains  his  maximum  elongation,  and  this  fact  ex 
ercises  a  more  important  effect  than  the  mere  amount  of 
elongation. 


78 


HALF-HOURS    WITH    THE    PLANETS. 


on  both  rods  spaces  each  subtending  a  degree  as 
seen  from  the  point  of  view.  Thus,  if  the  point  of 
view  is  9^  feet  off,  these  spaces  must  each  be  2  inches 
long,  and  they  must  be  proportionately  less  or  greater 
as  the  eye  is  nearer  or  farther. 


Fig.  10. 

Now  suppose  the  observer  wishes  to  view  Mercury 
on  some  day,  whereon  Mercury  is  an  evening  star. 
Take,  for  instance,  June  9th,  1868.  We  find  from 
'  Dietrich  sen '  that  on  this  day  (at  noon)  Mercury's 
E.  A.  is  6  h.  53  m.  23  s. :  and  the  sun's  5  h.  11  m. 
31  s.  We  need  not  trouble  ourselves  about  the 
odd  hours  after  noon,  and  thus  we  have  Mercury's 


HALF-HOURS   WITH    THE   PLANETS.  79 

R.  A.  greater  than  the  sun's  by  1  h.  41  m.  52  s.  Now 
we  will  suppose  that  the  observer  has  so  fixed  his 
uprights  and  the  two  rods,  that  the  sun,  seen  from 
the  fixed  point  of  view,  appears  to  pass  the  point  of 
crossing  of  the  rods  at  half-past  seven,  then  Mercury 
will  pass  the  cross-rod  at  llm.  52  s.  past  nine.  But 
where  ?  To  learn  this  we  must  take  out  Mercury's 
declination,  which  is  24°  43'  18"  N.,  and  the  sun's, 
which  is  22°  59'  10"  N.  The  difference,  1°  44'  8"  N. 
gives  us  Mercury's  place,  which  it  appears  is  rather 
less  than  1J  degree  north  of  the  sun.  Thus,  about 
1  h.  42  m.  after  the  sun  has  passed  the  cross-rod, 
Mercury  will  pass  it  between  tho  first  and  second 
divisions  above  the  point  of  fastening.  The  sun  will 
have  set  about  an  hour,  and  Mercury  will  be  easily 
found  when  the  telescope  is  directed  towards  tho 
place  indicated. 

It  will  be  noticed  that  this  method  does  not 
require  the  time  to  be  exactly  known.  All  we  have 
to  do  is  to  note  the  moment  at  which  the  sun  passes 
the  point  of  fastening  of  the  two  rods,  and  to  take 
our  1  h.  42  m.  from  that  moment. 

This  method,  it  may  be  noticed  in  passing,  may  be 
applied  to  give  naked-eye  observations  of  Mercury 
at  proper  seasons  (given  in  the  almanac).  By  a  little 
ingenuity  it  may  be  applied  as  well  to  morning  as  to 
evening  observations,  the  sun's  passage  of  the  cross- 
rod  being  taken  on  one  morning  and  Mercury's  on 
the  next,  so  many  minutes  before  the  hour  of  the  first 
observation.  In  this  way  several  views  of  Mercury 
may  be  obtained  during  the  year. 

Such  methods  may  appear  very  insignificant  to  the 
systematic  observer  with  the  equatorial,  but  that  they 
are  effective  I  can  assert  from  my  own  experience. 
Similar  methods  may  be  applied  to  determine  from 
the  position  of  a  known  object,  that  of  any  neigh 
bouring  unknown  object  even  at  night.  The  cross- 


80  HALF-HOURS    WITH    THE    PLANETS. 

rod  must  be  shifted  (or  else  two  cross-rods  used) 
when  the  unknown  precedes  the  known  object.  If 
two  cross-rods  are  used,  account  must  be  taken  of  the 
gradual  diminution  in  the  length  of  a  degree  of 
right  ascension  as  we  leave  the  equator. 

Even  simpler  methods  carefully  applied  may  serve 
to  give  a  view  of  Mercury.  To  show  this,  I  may 
describe  how  I  obtained  my  first  view  of  this  planet. 
On  June  1st,  1863,  I  noticed,  that  at  five  minutes 
past  seven  the  sun,  as  seen  from  my  study  window,  ap 
peared  from  behind  the  gable-end  of  Mr.  St.  Aubyn's 
house  at  Stoke,  Devon.  I  estimated  the  effect  of 
Mercury's  northerly  declination  (different  of  course 
for  a  vertical  wall,  than  for  the  cross-rod  in  fig. 
8,  which,  in  fact,  agrees  with  a  declination-circle), 
and  found  that  he  would  pass  out  opposite  a  par 
ticular  point  of  the  wall  a  certain  time  after  the  sun. 
I  then  turned  the  telescope  towards  that  point,  and 
focussed  for  distinct  vision  of  distant  objects,  so 
that  the  outline  of  the  house  was  seen  out  of  focus. 
As  the  calculated  time  of  apparition  approached, 
I  moved  the  telescope  up  and  down  so  that  the  field 
swept  the  neighbourhood  of  the  estimated  point  of 
apparition.  I  need  hardly  say  that  Mercury  did  not 
appear  exactly  at  the  assigned  point,  nor  did  I  see 
him  make  his  first  appearance  ;  but  I  picked  him  up 
so  soon  after  emergence  that  the  outline  of  the  house 
was  in  the  field  of  view  with  him.  He  appeared  as 
a  half-disc.  I  followed  him  with  the  telescope  until 
the  sun  had  set,  and  soon  after  I  was  able  to  see  him 
very  distinctly  with  the  naked  eye.  He  shone  with 
a  peculiar  brilliance  on  the  still  bright  sky;  but 
although  perfectly  distinct  to  the  view  when  his 
place  was  indicated,  he  escaped  detection  by  the  un 
directed  eye.* 

*  It  does  not  seein  to  me  that  the  difficulty  of  detecting 
Mercury  is  due  to  the  difficulty  "of  identifying  it  amongst 


HALF-HOURS    WITH    THE    PLANETS.  81 

Mercury  does  not  present  any  features  of  great 
interest  in  ordinary  telescopes ;  though  he  usually 
appears  better  denned  than  Venus,  at  least  as  the 
latter  is  seen  on  a  dark  sky.  The  phases  are  pleas 
ingly  seen  (as  shown  in  Plate  6)  with  a  telescope 
of  moderate  power.  For  their  proper  observation, 
however,  the  planet  must  be  looked  for  with  the 
telescope  in  the  manner  above  indicated,  as  he 
always  shows  a  nearly  semi-circular  disc  when  he 
is  visible  to  the  naked  eye. 

We  come  next  to  Venus,  the  most  splendid  of  all 
the  planets  to  the  eye.  In  the  telescope  Venus 
disappoints  the  observer,  however.  Her  intense 
lustre  brings  out  every  defect  of  the  instrument, 
and  especially  the  chromatic  aberration.  A  dark 
glass  often  improves  the  view,  but  not  always.  Be 
sides,  an  interposed  glass  has  an  unpleasant  effect  on 
the  field  of  view. 

Perhaps  the  best  method  of  observing  Venus 
is  to  search  for  her  when  she  is  still  high  above 
the  horizon,  and  when  therefore  the  background 
of  the  sky  is  bright  enough  to  take  off  the  planet's 
glare.  The  method  I  have  described  for  the  ob 
servation  of  Mercury  will  prove  very  useful  in  the 
search  for  Venus  when  the  sun  is  above  the  hori 
zon  or  but  just  set.  Of  course,  when  an  object  is 
to  be  looked  for  high  above  the  horizon,  the  two 
rods  which  support  the  cross-rods  must  not  be  up 
right,  but  square  to  the  line  of  view  to  that  part 
of  the  sky. 

But  the  observer  must  not  expect  to  see  much 
during  his  observation  of  Venus.  In  fact,  he  can 
scarcely  do  more  than  note  her  varying  phases  (see 

the  surrounding  stars,  during  the  short  time  that  it  can  be 
seen  "  (Hind's  '  Introduction  to  Astronomy ').  There  are 
few  stars  which  are  comparable  with  Mercury  in  brilliancy, 
when  seen  under  the  same  light. 


82  HALF-HOURS   WITH    THE   PLANETS. 

Plate  6)  and  the  somewhat  uneven  boundary  of  the 
terminator.  Our  leading  observers  have  done  so 
little  with  this  fascinating  but  disappointing  planet, 
that  amateurs  must  not  be  surprised  at  their  own 
failure. 

I  suppose  the  question  whether  Venus  has  a 
satellite,  or  at  any  rate  whether  the  object  supposed 
to  have  been  seen  by  Cassini  and  other  old  observers 
were  a  satellite,  must  be  considered  as  decided  in  the 
negative.  That  Cassini  should  have  seen  an  object 
which  Dawes  and  Webb  have  failed  to  see  must  be 
considered  utterly  improbable. 

Leaving  the  inferior  planets,  we  come  to  a  series 
of  important  and  interesting  objects. 

First  we  have  the  planet  Mars,  nearly  the  last  in 
the  scale  of  planetary  magnitude,  but  far  from  being 
the  least  interesting  of  the  planets.  It  is  in  fact 
quite  certain  that  we  obtain  a  better  view  of  Mars 
than  of  any  object  in  the  heavens,  save  the  Moon 
alone.  He  may  present  a  less  distinguished  ap 
pearance  than  Jupiter  or  Saturn,  but  we  see  his  sur 
face  on  a  larger  scale  than  that  of  either  of  those 
giant  orbs,  even  if  we  assume  that  we  ever  obtain  a 
fair  view  of  their  real  surface. 

Nor  need  the  moderately  armed  observer  despair 
of  obtaining  interesting  views  of  Mars.  The  tele 
scope  with  which  Beer  and  Madler  made  their  cele 
brated  series  of  views  was  only  a  4-inch  one,  so 
that  with  a  3-inch  or  even  a  2-inch  aperture  the 
attentive  observer  may  expect  interesting  views.  In 
fact,  more  depends  on  the  observer  than  on  the  in 
strument.  A  patient  and  attentive  scrutiny  will 
reveal  features  which  at  the  first  view  wholly  escape 
notice. 

In  Plate  6  I  have  given  a  series  of  views  of  Mars 
much  more  distinct  than  an  observer  may  expect  to 
obtain  with  moderate  powers.  I  add  a  chart  of  Mars-,  a 


HALF-HOURS    WITH    THE    PLANETS.  83 

miniature  of  one  I  have  prepared  from  a  charming 
series  of  tracings  supplied  me  by  Mr.  Dawes.  The 
views  taken  by  this  celebrated  observer  in  1852 
1856,  I860,  1862,  and  1864,  are  far  better  than  any 
others  I  have  seen.  The  views  by  Beer  and  Madler 
are  good,  as  are  some  of  Secchi's  (though  they 
appear  badly  drawn),  Nasmyth's  and  Phillips'; 
Delarue's  two  views  are  also  admirable ;  and  Lockyer 
has  given  a  better  set  of  views  than  any  of  the 
others.  But  there  is  an  amount  of  detail  in  Mr. 
Dawes'  views  which  renders  them  superior  to  any 
yet  taken.  I  must  confess  I  failed  at  a  first  view  to 
see  the  full  value  of  Mr.  Dawes'  tracings.  Faint 
marks  appeared,  which  I  supposed  to  be  merely 
intended  to  represent  shadings  scarcely  seen.  A 
more  careful  study  shewed  me  that  every  mark  is  to 
be  taken  as  the  representative  of  what  Mr.  Dawes 
actually  saw.  The  consistency  of  the  views  is  per 
fectly  wonderful,  when  compared  with  the  vagueness 
and  inconsistency  observable  in  nearly  all  other  views. 
And  this  consistency  is  not  shown  by  mere  re 
semblance,  which  might  have  been  an  effect  rather  of 
memory  (unconsciously  exerted)  than  observation. 
The  same  feature  changes  so  much  in  figure,  as  it 
appears  on  different  parts  of  the  disc,  that  it  was  some 
times  only  on  a  careful  projection  of  different  views 
that  I  could  determine  what  certain  features  near  the 
limb  represented.  But  when  this  had  been  done, 
and  the  distortion  through  the  effect  of  foreshorten 
ing  corrected,  the  feature  was  found  to  be  as  true  in 
shape  as  if  it  had  been  seen  in  the  centre  of  the 
planet's  disc. 

In  examining  Mr.  Dawes'  drawings  it  was  neces 
sary  that  the  position  of  Mars'  axis  should  be  known. 
The  data  for  determining  this  were  taken  from 
Dr.  Oudemann's  determinations  given  in  a  valuable 
paper  on  Mars  issued  from  Mr.  Bishop's  observatory. 

a  2 


84  HALF-HOURS   WITH    THE   PLANETS. 

But  instead  of  calculating  Mars'  presentation  by  the 
formulae  there  given,  I  found  it  convenient  rather  to 
make  use  of  geometrical  constructions  applied  to  my 
'  Charts  of  the  Terrestrial  Planets.'  Taking  Madler's 
start-point  for  Martial  longitudes,  that  is  the  longi 
tude-line  passing  near  Dawes'  forked  bay,  I  found 
that  my  results  agreed  pretty  fairly  with  those  in 
Prof.  Phillips'  map,  so  far  as  the  latter  went ;  but 
there  are  many  details  in  my  charts  not  found  in 
Prof.  Phillips'  nor  in  Madler's  earlier  charts. 

I  have  applied  to  the  different  features  the  names 
of  those  observers  who  have  studied  the  physical 
peculiarities  presented  by  Mars.  Mr.  Dawes'  name 
naturally  occurs  more  frequently  than  others.  In 
deed,  if  I  had  followed  the  rule  of  giving  to  each 
feature  the  name  of  its  discoverer,  Mr.  Dawes'  name 
would  have  occurred  much  more  frequently  than  it 
actually  does. 

On  account  of  the  eccentricity  of  his  orbit,  Mars 
is  seen  much  better  in  some  oppositions  than  in 
others.  When  best  seen  the  southern  hemisphere  is 
brought  more  into  view  than  the  northern  because 
the  summer  of  his  northern  hemisphere  occurs  when 
he  is  nearly  in  aphelion  (as  is  the  case  with  the 
Earth  by  the  way). 

The  relative  dimensions  and  presentation  of  Mars, 
as  seen  in  opposition  in  perihelion,  and  in  oppo 
sition  in  aphelion,  are  shown  in  the  two  rows  of 
figures. 

In  and  near  quadrature  Mars  is  perceptibly  gib 
bous.  He  is  seen  thus  about  two  months  before  or 
after  opposition.  In  the  former  case,  he  rises  late 
and  comes  to  the  meridian  six  hours  or  so  after 
midnight.  In  the  latter  case,  he  is  well  seen  in 
the  evening,  coming  to  the  meridian  at  six.  His 
appearance  and  relative  dimensions  as  he  passes 
from  opposition  to  quadrature  are  shown  in  the  last 
three  figures  of  the  upper  row. 


HALF-HOURS   WITH    THE    PLANETS.  85 

Mars'  polar  caps  may  be  seen  with  very  moderate 
powers. 

I  add  four  sets  of  meridians  (Plate  6),  by  filling 
in  which  from  the  charts  the  observer  may  obtain 
any  number  of  views  of  the  planet  as  it  appears  at 
different  times. 

Passing  over  the  asteroids,  which  are  not  very  in 
teresting  objects  to  the  amateur  telescopist,  we  come 
to  Jupiter,  the  giant  of  the  solar  system,  surpassing 
our  Earth  more  than  1400  times  in  volume,  and  over- 
weighing  all  the  planets  taken  together  twice  over. 

Jupiter  is  one  of  the  easiest  of  all  objects  of 
telescopic  observation.  No  one  can  mistake  this 
orb  when  it  shines  on  a  dark  sky,  and  only  Venus 
can  be  mistaken  for  it  when  seen  as  a  morning  or 
evening  star.  Sometimes  both  are  seen  together 
on  the  twilight  sky,  and  then  Venus  is  generally  the 
brighter.  Seen,  however,  at  her  brightest  and  at 
her  greatest  elongation  from  the  sun,  her  splendour 
scarcely  exceeds  that  with  which  Jupiter  shines 
when  high  above  the  southern  horizon  at  midnight. 

Jupiter's  satellites  may  be  seen  with  very  low 
powers ;  indeed  the  outer  ones  have  been  seen  with 
the  naked  eye,  and  all  are  visible  in  a  good  opera- 
glass.  Their  dimensions  relatively  to  the  disc  are 
shown  in  Plate  7.  Their  greatest  elongations  are 
compared  with  the  disc  in  the  low-power  view. 

Jupiter's  belts  may  also  be  well  seen  with  mo 
derate  telescopic  power.  The  outer  parts  of  his 
disc  are  perceptibly  less  bright  than  the  centre. 

More  difficult  of  observation  are  the  transits  of 
the  satellites  and  of  their  shadows.  Still  the  atten 
tive  observer  can  see  the  shadows  with  an  aperture 
of  two  inches,  and  the  satellites  themselves  with  an 
aperture  of  three  inches. 

The  minute  at  which  the  satellites  enter  on  the 
disc,  or  pass  off,  is  given  in  '  Dietrichsen's  Al- 


86  HALF-HOURS    WITH    THE    PLANETS. 

manac.'  The  '  Nautical  Almanac '  also  gives  the 
corresponding  data  for  the  shadows. 

The  eclipses  of  the  satellites  in  Jupiter's  shadow, 
and  their  occultations  by  his  disc,  are  also  given  in 
'  Dietrichsen's  Almanac.' 

In  the  inverting  telescope  the  satellites  move  from 
right  to  left  in  the  nearer  parts  of  their  orbit,  and 
therefore  transit  Jupiter's  disc  in  that  direction, 
and  from  left  to  right  in  the  farther  parts.  Also 
note  that  before  opposition,  (i.)  the  shadows  travel 
in  front  of  the  satellites  in  transiting  the  disc ;  (ii.) 
the  satellites  are  eclipsed  in  Jupiter's  shadow ;  (iii.) 
they  reappear  from  behind  his  disc.  On  the  other 
hand,  after  opposition,  (i.)  the  shadows  travel  behind 
the  satellites  in  transiting  the  disc ;  (ii.)  the  satel 
lites  are  occulted  by  the  disc;  (iii.)  they  reappear 
from  eclipse  in  Jupiter's  shadow. 

Conjunctions  of  the  satellites  are  common  phe 
nomena,  and  may  be  waited  for  by  the  observer  who 
sees  the  chance.  An  eclipse  of  one  satellite  by  the 
shadow  of  another  is  not  a  common  phenomenon ; 
in  fact,  I  have  never  heard  of  such  an  eclipse  being 
seen.  That  a  satellite  should  be  quite  extinguished 
by  another's  shadow  is  a  phenomenon  not  absolutely 
impossible,  but  which  cannot  happen  save  at  long 
intervals. 

The  shadows  are  not  black  spots  as  is  erroneously 
stated  in  nearly  all  popular  works  on  astronomy. 
The  shadow  of  the  fourth,  for  instance,  is  nearly  all 
penumbra,  the  really  black  part  being  quite  minute 
by  comparison.  The  shadow  of  the  third  has  a 
considerable  penumbra,  and  even  that  of  the  first 
is  not  wholly  black.  These  penumbras  may  not  be 
perceptible,  but  they  affect  the  appearance  of  the 
shadows.  For  instance,  the  shadow  of  the  fourth 
is  perceptibly  larger  but  less  black  than  that  of  the 
third,  though  the  third  is  the  larger  satellite. 


HALF-HOURS    WITH    THE    PLANETS.  87 

In  transit  the  first  satellite  moves  fastest,  the 
fourth  slowest,  the  others  in  their  order.  The 
shadow  moves  just  as  fast  (appreciably)  as  the  sa 
tellite  it  belongs  to.  Sometimes  the  shadow  of  the 
satellite  may  be  seen  to  overtake  (apparently)  the  disc 
of  another.  In  such  a  case  the  shadow  does  not 
pass  over  the  disc,  but  the  disc  conceals  the  shadow. 
This  is  explained  by  the  fact  that  the  shadow,  if 
visible  throughout  its  length,  would  be  a  line  reach 
ing  slantwise  from  the  satellite  it  belongs  to,  and 
the  end  of  the  shadow  (that  is,  the  point  where  it 
meets  the  disc)  is  not  the  point  where  the  shadow 
crosses  the  orbit  of  any  inner  satellite.  Thus  the 
latter  may  be  interposed  between  the  end  of  the  sha 
dow — the  only  part  of  the  shadow  really  visible — 
and  the  eye ;  but  the  end  of  the  shadow  cannot  be 
interposed  between  the  satellite  and  the  eye.  If  a 
satellite  on  the  disc  were  eclipsed  by  another  satel 
lite,  the  black  spot  thus  formed  would  be  in  another 
place  from  the  black  spot  on  the  planet's  body.  I 
mention  all  this  because,  simple  as  the  question 
may  seem,  I  have  known  careful  observers  to  make 
mistakes  on  this  subject.  A  shadow  is  seen  cross 
ing  the  disc  and  overtaking,  apparently,  a  satellite 
in  transit.  It  seems  therefore,  on  a  first  view,  that 
the  shadow  will  hide  the  satellite,  and  observers 
have  even  said  that  they  have  seen  this  happen. 
But  they  are  deceived.  It  is  obvious  that  if  one 
satellite  eclipse  another,  the  shadows  of  both  must  occupy 
the  same  point  on  Jupiter's  body.  Thus  it  is  the 
overtaking  of  one  shadow  by  another  on  the  disc, 
and  not  the  overtaking  of  a  satellite  by  a  shadow, 
which  determines  the  occurrence  of  that  as  yet 
unrecorded  phenomenon,  the  eclipse  of  one  satellite 
by  another.* 

*  I  may  notice  another  error  sometimes  made.  It  is  said 
that  the  shadow  of  a  satellite  appears  elliptical  when  near 


88  HALF-HOUKS   WITH    THE    PLANETS. 

The  satellites  when  far  from  Jupiter  seem  to  lie 
in  a  straight  line  through  his  centre.  But  as  a 
matter  of  fact  they  do  not  in  general  lie  in  an  exact 
straight  line.  If  their  orbits  could  be  seen  as  lines 
of  light,  they  would  appear,  in  general,  as  very  long 
ellipses.  The  orbit  of  the  fourth  would  frequently 
be  seen  to  be  quite  clear  of  Jupiter's  disc,  and  the 
orbit  of  the  third  might  in  some  very  exceptional 
instances  pass  just  clear  of  the  disc.  The  satellites 
move  most  nearly  in  a  straight  line  (apparently) 
when  Jupiter  comes  to  opposition  in  the  beginning 
of  February  or  August,  and  they  appear  to  depart 
most  from  rectilinear  motion  when  opposition  occurs 
in  the  beginning  of  May  and  November.  At  these 
epochs  the  fourth  satellite  may  be  seen  to  pass  above 
and  below  Jupiter's  disc  at  a  distance  equal  to  about 
one-sixth  of  the  disc's  radius. 

The  shadows  do  not  travel  in  the  same  apparent 
paths  as  the  satellites  themselves  across  the  disc, 
but  (in  an  inverting  telescope)  below  from  August 
to  January,  and  above  from  February  to  July. 

We  come  now  to  the  most  charming  telescopic 
object  in  the  heavens — the  planet  Saturn.  Inferior 
only  to  Jupiter  in  mass  and  volume,  this  planet 
surpasses  him  in  the  magnificence  of  his  system. 
Seen  in  a  telescope  of  adequate  power,  Saturn  is 
an  object  of  surpassing  loveliness.  He  must  be  an 
unimaginative  man  who  can  see  Saturn  for  the 
first  time  in  such  a  telescope,  without  a  feeling 
of  awe  and  amazement.  If  there  is  any  object  in 
the  heavens — I  except  not  even  the  Sun — calcu 
lated  to  impress  one  with  a  sense  of  the  wisdom 

the  edge  of  the  disc.  The  shadow  is  in  reality  elliptical 
when  thus  situated,  but  appears  circular.  A  moment's  con 
sideration  will  show  that  this  should  be  so.  The  part  of  the 
disc  concealed  by  a  satellite  near  the  limb  is  also  elliptical, 
but  of  course  appears  round. 


HALF-HOURS   WITH    THE   PLANETS.  89 

and  omnipotence  of  the  Creator  it  is  this.  "His 
fashioning  hand  "  is  indeed  visible  throughout  space, 
but  in  Saturn's  system  it  is  most  impressively 
manifest. 

Saturn,  to  be  satisfactorily  seen,  requires  a  much 
more  powerful  telescope  than  Jupiter.  A  good 
2-inch  telescope  will  do  much,  however,  in  exhi 
biting  his  rings  and  belts.  I  have  never  seen  him 
satisfactorily  myself  with  such  an  aperture,  but 
Mr.  Grover  has  not  only  seen  the  above-named 
features,  but  even  a  penumbra  to  the  shadow  on  the 
rings  with  a  2-inch  telescope. 

Saturn  revolving  round  the  sun  in  a  long  period 
—nearly  thirty  years — presents  slowly  varying 
changes  of  appearance  (see  Plate  7).  At  one  time 
the  edge  of  his  ring  is  turned  nearly  towards  the 
earth;  seven  or  eight  years  later  his  rings  are  as 
much  open  as  they  can  ever  be ;  then  they  gradu 
ally  close  up  during  a  corresponding  interval ;  open 
out  again,  exhibiting  a  different  face;  and  finally  close 
up  as  first  seen.  The  last  epoch  of  greatest  open 
ing  occurred  in  1856,  the  next  occurs  in  1870 :  the 
last  epoch  of  disappearance  occurred  in  1862-63, 
the  next  occurs  in  1879.  The  successive  views  ob 
tained  are  as  in  Plate  7  in  order  from  right  to  left, 
then  back  to  the  right-hand  figure  (but  sloped  the 
other  way) ;  inverting  the  page  we  have  this  figure 
thus  sloped,  and  the  following  changes  are  now 
indicated  by  the  other  figures  in  order  back  to  the 
first  (but  sloped  the  other  way  and  still  inverted), 
thus  returning  to  the  right-hand  figure  as  seen 
without  inversion. 

The  division  in  the  ring  can  be  seen  in  a  good 
2-inch  aperture  in  favourable  weather.  The  dark 
ring  requires  a  good  4-inch  and  good  weather. 

Saturn's  satellites  do  not,  like  Jupiter's,  form 
a  system  of  nearly  equal  bodies.  Titan,  the  sixth, 


90  HALF-HOURS   WITH   THE    PLANETS. 

is  probably  larger  than  any  of  Jupiter's  satellites, 
The  eighth  also  (Japetus)  is  a  large  body,  probably 
at  least  equal  to  Jupiter's  third  satellite.  But 
Rhea,  Dione,  and  Tethys  are  much  less  conspicuous, 
and  the  other  three  cannot  be  seen  without  more 
powerful  telescopes  than  those  we  are  here  dealing 
with. 

So  far  as  my  own  experience  goes,  I  consider  that 
the  five  larger  satellites  may  be  seen  distinctly  in 
good  weather  with  a  good  3J-inch  aperture.  I  have 
never  seen  them  with  such  an  aperture,  but  I  judge 
from  the  distinctness  with  which  these  satellites 
may  be  seen  with  a  4-inch  aperture.  Titan  is  gene 
rally  to  be  looked  for  at  a  considerable  distance 
from  Saturn — ahvays  when  the  ring  is  widely  open. 
Japetus  is  to  be  looked  for  yet  farther  from  the 
disc.  In  fact,  when  Saturn  comes  to  opposition  in 
perihelion  (in  winter  only  this  can  happen)  Japetus 
may  be  as  far  from  Saturn  as  one-third  of  the 
apparent  diameter  of  the  moon.  I  believe  that 
under  these  circumstances,  or  even  under  less  fa 
vourable  circumstances,  Japetus  could  be  seen  with 
a  good  opera-glass.  So  also  might  Titan. 

Transits,  eclipses,  and  occulations  of  Saturn's 
satellites  can  only  be  seen  when  the  ring  is  turned 
nearly  edgewise  towards  the  earth.  For  the  orbits 
of  the  seven  inner  satellites  lying  nearly  in  the 
plane  of  the  rings  would  (if  visible  throughout  their 
extent)  then  only  appear  as  straight  lines,  or  as 
long  ellipses  cutting  the  planet's  disc. 

The  belts  on  Saturn  are  not  very  conspicuous. 
A  good  3^-inch  is  required  (so  far  as  my  experience 
extends)  to  show  them  satisfactorily. 

The  rings  when  turned  edgewise  either  towards 
the  earth  or  sun,  are  not  visible  in  ordinary  tele 
scopes,  neither  can  they  be  seen  when  the  earth  and 
sun  are  on  opposite  sides  of  the  rings.  In  powerful 


HALF-HOURS   WITH    THE   PLANETS.  91 

telescopes  the  rings  seem  never  entirely  to  dis 
appear. 

The  shadow  of  the  planet  on  the  rings  may  be 
well  seen  with  a  good  2-inch  telescope,  which  will 
also  show  Ball's  division  in  the  rings.  The  shadow 
of  the  rings  on  the  planet  is  a  somewhat  more  diffi 
cult  feature.  The  shadow  of  the  planet  on  the  rings 
is  best  seen  when  the  rings  are  well  open  and  the 
planet  is  in  or  near  quadrature.  It  is  to  be  looked 
for  to  the  left  of  the  ball  (in  an  inverting  telescope) 
at  quadrature  preceding  opposition,  and  to  the  right 
at  quadrature  following  opposition.  Saturn  is  more 
likely  to  be  studied  at  the  latter  than  at  the  former 
quadrature,  as  in  quadrature  preceding  opposition 
he  is  a  morning  star.  The  shadow  of  the  rings  on 
the  planet  is  best  seen  when  the  rings  are  but  mode 
rately  open,  and  Saturn  is  in  or  near  quadrature. 
When  the  shadow  lies  outside  the  rings  it  is  best 
seen,  as  the  dark  ring  takes  off  from  the  sharpness 
of  the  contrast  when  the  shadow  lies  within  the 
ring.  It  would  take  more  space  than  I  can  spare 
here  to  show  how  it  is  to  be  determined  (independ 
ently)  whether  the  shadow  lies  within  or  without 
the  ring.  But  the  '  Nautical  Almanac '  gives  the 
means  of  determining  this  point.  When,  in  the 
table  for  assigning  the  appearance  of  the  rings,  / 
is  less  than  /'  the  shadow  lies  outside  the  ring, 
when  /  is  greater  than  /'  the  shadow  lies  within 
the  ring. 

Uranus  is  just  visible  to  the  naked  eye  when  he 
is  in  opposition,  and  his  place  accurately  known. 
But  he  presents  no  phenomena  of  interest.  I  have 
seen  him  under  powers  which  made  his  disc  nearly 
equal  to  that  of  the  moon,  yet  could  see  nothing 
but  a  faint  bluish  disc. 

Neptune  also  is  easily  found  if  his  place  be  accu- 


92  HALF-HOURS    WITH    THE    PLANETS. 

rately  noted  on  a  map,  and  a  good  finder  used.  We 
have  only  to  turn  the  telescope  to  a  few  stars  seen 
in  the  finder  nearly  in  the  place  marked  in  our  map, 
and  presently  we  shall  recognise  the  one  we  want 
by  the  peculiarity  of  its  light.  What  is  the  lowest 
power  which  will  exhibit  Neptune  as  a  disc  I  do 
not  know,  but  I  am  certain  no  observer  can  mis 
take  him  for  a  fixed  star  with  a  2-inch  aperture 
and  a  few  minutes'  patient  scrutiny  in  favourable 
weather. 


PLATE  TJ 


*». 


Solar     Spote 


FI-OOJ    dri»4rija|a    by 
Her  P  Hov?leU. 


HALF-HOURS    WITH    THE   SUN   AND -MOON.  93 


CHAPTEK  VII. 


HALF-HOUES  WITH  THE  SUN  AND  MOON. 

THE  Moon  perhaps  is  the  easiest  of  all  objects  of 
telescopic  observation.  A  very  moderate  telescope 
will  show  her  most  striking  features,  while  each  in 
crease  of  power  is  repaid  by  a  view  of  new  details. 
Yet  in  one  sense  the  moon  is  a  disappointing  object 
even  to  the  possessor  of  a  first-class  instrument.  For 
the  most  careful  and  persistent  scrutiny,  carried  on 
for  a  long  series  of  years,  too  often  fails  to  reward 
the  observer  by  any  new  discoveries  of  interest.  Our 
observer  must  therefore  rather  be  prepared  to  enjoy 
the  observation  of  recognised  features  than  expect  to 
add  by  his  labours  to  our  knowledge  of  the  earth's 
nearest  neighbour. 

Although  the  moon  is  a  pleasing  and  surprising 
telescopic  object  when  full,  the  most  interesting  views 
of  her  features  are  obtained  at  other  seasons.  If 
we  follow  the  moon  as  she  waxes  or  wanes,  we  see 
the  true  nature  of  that  rough  and  bleak  mountain 
scenery,  which  when  the  moon  is  full  is  partially 
softened  through  the  want  of  sharp  contrasts  of 
light  and  shadow.  If  we  watch,  even  for  half  an 
hour  only,  the  changing  form  of  the  ragged  line 
separating  light  from  darkness  on  the  moon's  disc, 
we  cannot  fail  to  be  interested.  "  The  outlying  and 
isolated  peak  of  some  great  mountain-chain  becomes 
gradually  larger,  and  is  finally  merged  in  the  gene 
ral  luminous  surface ;  great  circular  spaces,  enclosed 
with  rough  and  rocky  walls  many  miles  in  diameter, 
become  apparent ;  some  with  flat  and  perfectly 


94     HALF-HOURS  WITH  THE  SUN  AND  MOON. 

smooth  floors,  variegated  with  streaks;  others  in 
which  the  flat  floor  is  dotted  with  numerous  pits 
or  covered  with  broken  fragments  of  rock.  Occa 
sionally  a  regularly-formed  and  unusually  sym 
metrical  circular  formation  makes  its  appearance ; 
the  exterior  surface  of  the  wall  bristling  with  ter 
races  rising  gradually  from  the  plain,  the  interior 
one  much  m'ore  steep,  and  instead  of  a  flat  floor,  the 
inner  space  is  concave  or  cup-shaped,  with  a  solitary 
peak  rising  in  the  centre.  Solitary  peaks  rise  from 
the  level  plains  and  cast  their  long  narrow  shadows 
athwart  the  smooth  surface.  Vast  plains  of  a  dusky 
tint  become  visible,  not  perfectly  level,  but  covered 
with  ripples,  pits,  and  projections.  Circular  wells, 
which  have  no  surrounding  wall  dip  below  the  plain, 
and  are  met  with  even  in  the  interior  of  the  circular 
mountains  and  on  the  tops  of  their  walls.  From 
some  of  the  mountains  great  streams  of  a  brilliant 
white  radiate  in  all  directions  and  can  be  traced  for 
hundreds  of  miles.  We  see,  again,  great  fissures, 
almost  perfectly  straight  and  of  great  length,  al 
though  very  narrow,  which  appear  like  the  cracks 
in  moist  clayey  soil  when  dried  by  the  sun."  * 

But  interesting  as  these  views  may  be,  it  was  not 
for  such  discoveries  as  these  that  astronomers  ex 
amined  the  surface  of  the  moon.  The  examination 
of  mere  peculiarities  of  physical  condition  is,  after 
all,  but  barren  labour,  if  it  lead  to  no  discovery  of 
physical  variation.  The  principal  charm  of  astro 
nomy,  as  indeed  of  all  observational  science,  lies  in 
the  study  of  change — of  progress,  development,  and 
decay,  and  specially  of  systematic  variations  taking 
place  in  regularly-recurring  cycles.  And  it  is  in 
this  relation  that  the  moon  has  been  so  disappoint 
ing  an  object  of  astronomical  observation.  For  two 

*  From  a  paper  by  Mr.  Breen,  in  the  '  Popular  Science 
Review/  October,  1864. 


HALF-HOURS   WITH    THE    SUN    AND    MOON.  95 

centuries  and  a  half  her  face  has  been  scanned  with 
the  closest  possible  scrutiny ;  her  features  have 
been  portrayed  in  elaborate  maps ;  many  an  astro 
nomer  has  given  a  large  portion  of  his  life  to  the 
work  of  examining  craters,  plains,  mountains,  and 
valleys,  for  the  signs  of  change ;  but  until  lately  no 
certain  evidence — or  rather,  no  evidence  save  of  the 
most  doubtful  character — has  been  afforded  that 
the  moon  is  other  than  "  a  dead  and  useless  waste 
of  extinct  volcanoes."  Whether  the  examination  of 
the  remarkable  spot  called  Linne  —  where  lately 
signs  were  supposed  to  have  been  seen  of  a  process 
of  volcanic  eruption — will  prove  an  exception  to 
this  rule,  remains  to  be  seen.  The  evidence  seems 
to  me  strongly  to  favour  the  supposition  of  a  change 
of  some  sort  having  taken  place  in  this  neighbour 
hood. 

The  sort  of  scrutiny  required  for  the  discovery 
of  changes,  or  for  the  determination  of  their  extent, 
is  far  too  close  and  laborious  to  be  attractive  to 
the  general  observer.  Yet  the  kind  of  observation 
which  avails  best  for  the  purpose  is  perhaps  also  the 
most  interesting  which  he  can  apply  to  the  lunar 
details.  The  peculiarities  presented  by  a  spot  upon 
the  moon  are  to  be  observed  from  hour  to  hour  (or 
from  day  to  day,  according  to  the  size  of  the  spot) 
as  the  sun's  light  gradually  sweeps  across  it,  until 
the  spot  is  fully  lighted ;  then  as  the  moon  wanes 
and  the  sun's  light  gradually  passes  from  the  spot, 
the  series  of  observations  is  to  be  renewed.  A  comr 
parison  of  them  is  likely — especially  if  the  observer 
is  a  good  artist  and  has  executed  several  faithful 
delineations  of  the  region  under  observation,  to 
throw  much  light  upon  the  real  contour  of  the 
moon's  surface  at  this  point. 

In  the  two  lunar  views  in  Plate  7  some  of  the 
peculiarities  I  have  described  are  illustrated.  But 


96     HALF-HOURS  WITH  THE  SUN  AND  MOON. 

the  patient  observer  will  easily  be  able  to  construct 
for  himself  a  set  of  interesting  views  of  different 
regions. 

It  may  be  noticed  that  for  observation  of  the 
waning  moon  there  is  no  occasion  to  wait  for  those 
hours  in  which  only  the  waning  moon  is  visible 
during  the  night.  Of  course  for  the  observation  of 
a  particular  region  under  a  particular  illumination, 
the  observer  has  no  choice  as  to  hour.  But  for 
generally  interesting  observations  of  the  waning 
moon  he  can  wait  till  morning  and  observe  by  day 
light.  The  moon  is,  of  course,  very  easily  found  by 
the  unaided  eye  (in  the  day  time)  when  not  very 
near  to  the  sun ;  and  the  methods  described  in 
Chapter  V.  will  enable  the  observer  to  find  the 
moon  when  she  is  so  near  to  the  sun  as  to  present 
the  narrowest  possible  sickle  of  light. 

One  of  the  most  interesting  features  of  the  moon, 
when  she  is  observed  with  a  good  telescope,  is  the 
variety  of  colour  presented  by  different  parts  of  her 
surface.  We  see  regions  of  the  purest  white — 
regions  which  one  would  be  apt  to  speak  of  as  snow- 
covered,  if  one  could  conceive  the  possibility  that 
snow  should  have  fallen  where  (now,  at  least)  there 
is  neither  air  nor  water.  Then  there  are  the  so- 
called  seas,  large  grey  e>r  neutral-tinted  regions, 
differing  from  the  former  not  merely  in  colour  and 
in  tone,  but  in  the  photographic  quality  of  the  light 
they  reflect  towards  the  earth.  Some  of  the  seas 
exhibit  a  greenish  tint,  as  the  Sea  of  Serenity  and  the 
Sea  of  Humours.  Where  there  is  a  central  moun 
tain  within  a  circular  depression,  the  surrounding 
plain  is  generally  of  a  bluish  steel-grey  colour. 
There  is  a  region  called  the  Marsli  of  Sleep,  which 
exhibits  a  pale  red  tint,  a  colour  seen  also  near  the 
Hyrcinian  mountains,  within  a  circumvallation  called 
Lichtenburg.  The  brightest  portion  of  the  whole 


HALF-HOURS   WITH    THE    SUN    AND    MOON.  97 

lunar  disc  is  Aristarchus,  the  peaks  of  which  shine 
often  like  stars,  when  the  mountain  is  within  the 
unillumined  portion  of  the  moon.  The  darkest 
regions  are  Grimaldi  and  Endymion  and  the  great 
plain  called  Plato  by  modern  astronomers — but,  by 
Hevelius,  the  Greater  Black  Lake. 

THE  SUN. — Observation  of  the  sun  is  perhaps  on 
the  whole  the  most  interesting  work  to  which  the 
possessor  of  a  moderately  good  telescope  can  apply 
his  instrument.  Those  wonderful  varieties  in  the 
appearance  of  the  solar  surface  which  have  so  long 
perplexed  astronomers,  not  only  supply  in  them 
selves  interesting  subjects  of  observation  and  exa 
mination,  but  gain  an  enhanced  meaning  from  the 
consideration  that  they  speak  meaningly  to  us  of 
the  structure  of  an  orb  which  is  the  source  of  light 
and  heat  enjoyed  by  a  series  of  dependent  worlds 
whereof  our  earth  is — in  size  at  least — a  compara 
tively  insignificant  member.  Swayed  by  the  attrac 
tion  of  this  giant  globe,  Jupiter  and  Saturn,  Uranus 
and  Neptune,  as  well  as  the  four  minor  planets,  and 
the  host  of  asteroids,  sweep  continuously  in  their 
appointed  orbits,  in  ever  new  but  ever  safe  and 
orderly  relations  amongst  each  other.  If  the  sun's 
light  and  heat  were  lost,  all  life  and  work  among 
the  denizens  of  these  orbs  would  at  once  cease ;  if 
his  attractive  energy  were  destroyed,  these  orbs 
would  cease  to  form  a  system. 

The  sun  may  be  observed  conveniently  in  many 
ways,  some  more  suited  to  the  general  observer  who 
has  not  time  or  opportunity  for  systematic  observa 
tion  ;  others  more  instructive,  though  involving  more 
of  preparation  and  arrangement. 

The  simplest  method  of  observing  the  sun  is  to 
use  the  telescope  in  the  ordinary  manner,  protect 
ing  the  eye  by  means  of  dark-green  or  neutral- 
tinted  glasses.  Some  of  the  most  interesting  views 

H 


98  HALF-HOUKS    WITH    THE    SUN   AND    MOON. 

I  have  ever  obtained  of  the  sun,  have  resulted  from 
the  use  of  the  ordinary  terrestrial  or  erecting  eye 
piece,  capped  with  a  dark  glass.  The  magnifying 
power  of  such  an  eye-piece  is,  in  general,  much 
lower  than  that  available  with  astronomical  eye 
pieces.  But  vision  is  very  pleasant  and  distinct 
when  the  sun  is  thus  observed,  and  a  patient  scrutiny 
reveals  almost  every  feature  which  the  highest  as 
tronomical  power  applicable  could  exhibit.  Then, 
owing  to  the  greater  number  of  intervening  lenses, 
there  is  not  the  same  necessity  for  great  darkness  or 
thickness  in  the  coloured  glass,  so  that  the  colours 
of  the  solar  features  are  seen  much  more  satis 
factorily  than  when  astronomical  eye-pieces  are 
employed. 

In  using  astronomical  eye-pieces  it  is  convenient 
to  have  a  rotating  wheel  attached,  by  which  dark 
ening  glasses  of  different  power  may  be  brought 
into  use  as  the  varying  illumination  may  require. 

Those  who  wish  to  observe  carefully  and  closely 
a  minute  portion  of  the  solar  disc,  should  employ 
Dawes'  eye-piece :  in  this  a  metallic  screen  placed 
in  the  focus  keeps  away  all  light  but  such  as  passes 
through  a  minute  hole  in  the  diaphragm. 

Another  convenient  method  of  diminishing  the 
light  is  to  use  a  glass  prism,  light  being  partially 
reflected  from  one  of  the  exterior  surfaces,  while  the 
refracted  portion  is  thrown  out  at  another. 

Very  beautiful  and  interesting  views  may  be  ob 
tained  by  using  such  a  pyramidal  box  as  is  depicted 
in  fig.  11. 

This  box  should  be  made  of  black  cloth  or  calico 
fastened  over  a  light  framework  of  wire  or  cane. 
The  base  of  the  pyramid  should  be  covered  on  the 
inside  with  a  sheet  of  white  glazed  paper,  or  with 
some  other  uniform  white  surface.  (Captain  Noble, 
I  believe,  makes  use  of  a  surface  of  plaster  of  Paris, 


HALF-HOURS    WITH    THE    SUN    AND    MOON.  *        99 


Fig.  11. 

smoothed  while  wet  with  plate-glass.  The  door  6  c 
enables  the  observer  to  "  change  power "  without 
removing  the  box,  while  larger  doors,  de  and  g  /, 
enable  him  to  examine  the  image ;  a  dark  cloth, 
such  as  photographers  use,  being  employed,  if  ne 
cessary,  to  keep  out  extraneous  light.  The  image 
may  also  be  examined  from  without,  if  the  bottom 
of  the  pyramid  be  formed  of  a  sheet  of  cut-glass  or 
oiled  tissue-paper. 

When  making  use  of  the  method  just  described, 
it  is  very  necessary  that  the  telescope-tube  should 
be  well  balanced.  A  method  by  "which  this  may  be 
conveniently  accomplished  has  been  already  de 
scribed  in  Chapter  I. 

But,  undoubtedly,  for  the  possessor  of  a  mode 
rately  good  telescope  there  is  no  way  of  viewing 
the  sun's  features  comparable  to  that  now  to  be 
described,  which  has  been  systematically  and  suc 
cessfully  applied  for  a  long  series  of  years  by  the 
Rev.  F.  Howlett.  To  use  his  own  words :  "  Any 
one  possessing  a  good  achromatic  of  not  more  than 
three  inches'  aperture,  who  has  a  little  dexterity 
with  his  pencil,  and  a  little  time  at  his  disposal  (all 
the  better  if  it  be  at  a  somewhat  early  hour  of  the 
morning)  "  may  by  this  method  "  deliberately  an?* 
satisfactorily  view,  measure,  and  (if  skill  suffice) 

H  2 


100      'HALF-HOURS    WITH    THE    SUN    AND    MOON. 

delineate  most  of  those  interesting  and  grand  solar 
phenomena  of  which  he  may  have  read,  or  which 
he  may  have  seen  depicted,  in  various  works  on 
physical  astronomy."  * 

The  method  in  question  depends  on  the  same 
property  which  is  involved  in  the  use  of  the  py 
ramidal  box  just  described,  supplemented  (where 
exact  and  systematic  observation  is  required)  by 
the  fact  that  objects  lying  on  or  between  the  lenses 
of  the  eye-piece  are  to  be  seen  faithfully  projected 
on  the  white  surface  on  which  the  sun's  image  is 
received.  In  place,  however,  of  a  box  carried  upon 
the  telescope-tube,  a  darkened  room  (or  true  camera 
obscura)  contains  the  receiving  sheet. 

A  chamber  is  to  be  selected,  having  a  window 
looking  towards  the  south — a  little  easterly,  if  pos 
sible,  so  as  to  admit  of  morning  observation.  All 
windows  are  to  be  completely  darkened  save  one, 
through  which  the  telescope  is  directed  towards  the 
sun.  An  arrangement  is  to  be  adopted  for  prevent 
ing  all  light  from  entering  by  this  window  except 
such  light  as  passes  down  the  tube  of  the  telescope. 
This  can  readily  be  managed  with  a  little  ingenuity. 
Mr.  Hewlett  describes  an  excellent  method.  The 
following,  perhaps,  will  sufficiently  serve  the  pur 
poses  of  the  general  observer  :  —  A  plain  frame 
(portable)  is  to  be  constructed  to  fit  into  the  window  : 
to  the  four  sides  of  this  frame  triangular  pieces  of 
cloth  (impervious  to  light)  are  to  be  attached,  their 
shape  being  such  that  when  their  adjacent  edges  are 
sewn  together  and  the  flaps  stretched  out,  they  form 
a  rectangular  pyramid  of  which  the  frame  is  the 
base.  Through  the  vertex  of  this  pyramid  (near 

*  '  Intellectual  Observer'  for  July,  1867,  to  which  magazine 
the  reader  is  referred  for  full  details  of  Mr.  Howlett's  method 
of  observation,  and  for  illustrations  of  the  appliances  he  made 
use  of,  and  of  some  of  his  results. 


HALF-HOURS  WITH  THE  SUN  AND  MOON.    101 

which,  of  course,  the  cloth  flaps  are  not  sewn  to 
gether)  the  telescope  tube  is  to  be  passed,  and  an 
elastic  cord  so  placed  round  the  ends  of  the  flaps 
as  to  prevent  any  light  from  penetrating  between 
them  and  the  telescope.  It  will  now  be  possible, 
without  disturbing  the  screen  (fixed  in  the  window), 
to  move  the  telscope  so  as  to  follow  the  sun  during 
the  time  of  observation.  And  the  same  arrangement 
will  serve  for  all  seasons,  if  so  managed  that  the 
elastic  cord  is  not  far  from  the  middle  of  the  tele 
scope-tube  ;  for  in  this  case  the  range  of  motion 
is  small  compared  to  the  range  of  the  tube's  ex 
tremity. 

A  large  screen  of  good  drawing-paper  should  next 
be  prepared.  This  should  be  stretched  on  a  light 
frame  of  wood,  and  placed  on  an  easel,  the  legs  of 
which  should  be  furnished  with  holes  and  pegs  that 
the  screen  may  be  set  at  any  required  height,  and 
be  brought  square  to  the  tube's  axis.  A  large 
T-square  of  light  wood  will  be  useful  to  enable  the 
observer  to  judge  whether  the  screen  is  properly 
situated  in  the  last  respect. 

We  wish  now  to  direct  the  tube  towards  the  sun, 
and  this  "  without  dazzling  the  eyes  as  by  the  ordi 
nary  method."  This  may  be  done  in  two  ways.  We 
may  either,  before  commencing  work — that  is,  before 
fastening  our  elastic  cord  so  as  to  exclude  all  light 
— direct  the  tube  so  that  its  shadow  shall  be  a  per 
fect  circle  (when  of  course  it  is  truly  directed),  then 
fasten  the  cord  and  afterwards  we  can  easily  keep 
the  sun  in  the  field  by  slightly  shifting  the  tube  as 
occasion  requires.  Or  (if  the  elastic  cord  has  already 
been  fastened)  we  may  remove  the  eye-tube  and 
shift  the  telescope -tube  about  —  the  direction  in 
which  the  sun  lies  being  roughly  known — until  we 
see  the  spot  of  light  received  down  the  telescope's 
axis  grow  brighter  and  brighter  and  finally  become 


102    HALF-HOURS  WITH  THE  SUN  AND  MOON. 

a  spot  of  sun-light.  If  a  card  be  held  near  the  focus 
of  the  telescope  there  will  be  seen  in  fact  an  image 
of  the  sun.  The  telescope  being  now  properly 
directed,  the  eye-tube  may  be  slipped  in  again,  and 
the  sun  may  be  kept  in  the  field  as  before. 

There  will  now  be  seen  upon  the  screen  a  picture 
of  the  sun  very  brilliant  and  pleasing,  but  perhaps 
a  little  out  of  focus.  The  focusing  should  therefore 
next  be  attended  to,  the  increase  of  clearness  in  the 
image  being  the  test  of  approach  to  the  true  focus. 
And  again,  it  will  be  well  to  try  the  effect  of  slight 
changes  of  distance  between  the  screen  and  the 
telescope's  eye-piece.  Mr.  Howlett  considers  one 
yard  as  a  convenient  distance  for  producing  an  ex 
cellent  effect  with  almost  any  eye-piece  that  the 
state  of  the  atmosphere  will  admit  of.  Of  course, 
the  image  becomes  more  sharply  defined  if  we 
bring  the  screen  nearer  to  the  telescope,  while  all  the 
details  are  enlarged  when  we  move  the  screen  away. 
The  enlargement  has  no  limits  save  those  depending 
on  the  amount  of  light  in  the  image.  But,  of 
course,  the  observer  must  not  expect  enlargement 
to  bring  with  it  a  view  of  new  details,  after  a  cer 
tain  magnitude  of  image  has  been  attained.  Still 
there  is  something  instructive,  I  think,  in  occasion 
ally  getting  a  very  magnified  view  of  some  re 
markable  spot.  I  have  often  looked  with  enhanced 
feelings  of  awe  and  wonder  on  the  gigantic  image 
of  a  solar  spot  thrown  by  means  of  the  diagonal 
eye-piece  upon  the  ceiling  of  the  observing-room. 
Blurred  and  indistinct  through  over-magnifying,  yet 
with  a  new  meaning  to  me,  there  the  vast  abysm  lies 
pictured ;  vague  imaginings  of  the  vast  and  incom 
prehensible  agencies  at  work  in  the  great  centre 
of  our  system  crowd  unbidden  into  my  mind ;  and 
I  seem  to  feel — not  merely  think  about — the  stu 
pendous  grandeur  of  that  life-emitting  orb. 


HALF-HOURS  WITH  THE  SUN  AND  MOON.    103 

To  return,  however,  to  observation  : — By  slightly 
shifting  the  tube,  different  parts  of  the  solar  disc 
can  be  brought  successively  upon  the  screen  and 
scrutinized  as  readily  as  if  they  were  drawn  upon  a 
chart.  "  With  a  power  of — say  about  60  or  80  linear 
— the  most  minute  solar  spot,  properly  so  called, 
that  is  capable  of  formation  "  (Mr.  Hewlett  believes 
"they  are  never  less  than  three  seconds  in  length 
or  breadth)  will  be  more  readily  detected  than  by 
any  other  method,"  see  Plate  7 ;  "as  also  will  any 
faculae,  mottling,  or  in  short,  any  other  phenomena 
that  may  then  be  existing  on  the  disc."  "  Drifting 
clouds  frequently  sweep  by,  to  vary  the  scene,  and 
occasionally  an  aerial  hail-  or  snow-  storm."  Mr. 
Hewlett  has  more  than  once  seen  a  distant  flight 
of  rooks  pass  slowly  across  the  disc  with  wonderful 
distinctness,  when  the  sun  has  been  at  a  low  alti 
tude,  and  likewise,  much  more  frequently,  the  rapid 
dash  of  starlings,  which,  very  much  closer  at  hand, 
frequent  his  church-tower." 

An  eclipse  of  the  sun,  or  a  transit  of  an  inferior 
planet,  is  also  much  better  seen  in  this  way  than  by 
any  other  method  of  observing  the  solar  disc.  In 
Plate  7  are  presented  several  solar  spots  as  they 
have  appeared  to  Mr.  Hewlett,  with  an  instrument 
of  moderate  power.  The  grotesque  forms  of  some  of 
these  are  remarkable ;  and  the  variations  the  spots 
undergo  from  day  to  day  are  particularly  interesting 
to  the  thoughtful  observer. 

A  method  of  measuring  the  spots  may  now  be 
described.  It  is  not  likely  indeed  that  the  ordinary 
observer  will  care  to  enter  upon  any  systematic 
series  of  measurements.  But  even  in  his  case,  the 
means  of  forming  a  general  comparison  between 
the  spots  he  sees  at  different  times  cannot  fail  to 
be  valuable.  Also  the  knowledge — which  a  simple 
method  of  measurement  supplies — of  the  actual  di- 


104        HALF-HOURS    WITH    THE    SUN    AND    MOON. 

mensions  of  a  spot  in  miles  (roughly)  is  calculated 
to  enhance  our  estimate  of  the  importance  of  these 
features  of  the  solar  disc.  I  give  Mr.  Hewlett's 
method  in  his  own  words  : — 

"  Cause  your  optician  to  rule  for  you  on  a  cir 
cular  piece  of  glass  a  number  of  fine  graduations, 
the  200th  part  of  an  inch  apart,  each  fifth  and  tenth 
line  being  of  a  different  length  in  order  to  assist  the 
eye  in  their  enumeration.  Insert  this  between 
the  anterior  and  posterior  lenses  of  a  Huygenian 
eye-piece  of  moderate  power,  say  80  linear.  Direct 
your  telescopo  upon  the  sun,  and  having  so  ar 
ranged  it  that  the  whole  disc  of  the  sun  may  be 
projected  on  the  screen,  count  carefully  the  number 
of  graduations  that  are  seen  to  exactly  occupy  the 
solar  diameter.  ...  It  matters  not  in  which  direc 
tion  you  measure  your  diameter,  provided  only  the 
sun  has  risen  some  18°  or  20°  above  the  horizon, 
and  so  escaped  the  distortion  occasioned  by  re 
fraction.* 

"  Next  let  us  suppose  that  our  observer  has  been 
observing  the  sun  on  any  day  of  the  year,  say,  if 
you  choose,  at  the  time  of  its  mean  apparent  dia 
meter,  namely  about  the  first  of  April  or  first  of 
October,  and  has  ascertained  that"  (as  is  the  case 
with  .Mr.  Howlett's  instrument)  "  sixty-four  gradu 
ations  occupy  the  diameter  of  the  projected  image. 
Now  the  semi-diameter  of  the  sun,  at  the  epochs 
above  mentioned,  according  to  the  tables  given  for 
every  day  of  the  year  in  the  '  Nautical  Almanac ' 

*  As  the  sun  does  not  attain  such  an  altitude  as  18°  during 
two  months  in  the  year,  it  is  well  to  notice  that  the  true 
length  of  the  sun's  apparent  solar  diameter  is  determinable 
even  immediately  after  sun-rise,  if  the  line  of  graduation  is 
made  to  coincide  with  the  horizontal  diameter  of  the  picture 
on  the  screen — for  refraction  does  not  affect  the  length  of 
this  diameter. 


HALF-HOURS  WITH  THE  SUN  AND  MOON.    105 

(the  same  as  in  Dietrichsen  and  Hannay's  very 
useful  compilation)  is  16'  2",  and  consequently  his 
mean  total  diameter  is  32'  4"  or  1924".  If  now  we 
divide  1924"  by  64"  this  will,  of  course,  award  as 
nearly  as  possible  30"  as  the  value  in  celestial  arc 
of  each  graduation,  either  as  seen  on  the  screen,  or 
as  applied  directly  to  the  sun  or  any  heavenly  body 
large  enough  to  be  measured  by  it." 

Since  the  sun's  diameter  is  about  850,000  miles, 
each  graduation  (in  the  case  above  specified)  corre 
sponds  to  one-64th  part  of  850,000  miles — that  is, 
to  a  length  of  13,256  miles  on  the  sun's  surface. 
Any  other  case  can  be  treated  in  precisely  the  same 
manner. 

It  will  be  found  easy  so  to  place  the  screen  that 
the  distance  between  successive  graduations  (as  seen 
projected  upon  the  screen)  may  correspond  to  any 
desired  unit  of  linear  measurement — say  an  inch. 
Then  if  the  observer  use  transparent  tracing-paper 
ruled  with  faint  lines  forming  squares  half-an-inch 
in  size,  he  can  comfortably  copy  directly  from  the 
screen  any  solar  phenomena  he  may  be  struck  with. 
A  variety  of  methods  of  drawing  will  suggest  them 
selves.  Mr.  Hewlett,  in  the  paper  I  have  quoted 
from  above,  describes  a  very  satisfactory  method, 
which  those  who  are  anxious  to  devote  themselves 
seriously  to  solar  observation  will  do  well  to  study. 

It  is  necessary  that  the  observer  should  be  able  to 
determine  approximately  where  the  sun's  equator  is 
situated  at  the  time  of  any  observation,  in  order 
that  he  may  assign  to  any  spot  or  set  of  spots  its 
true  position  in  relation  to  solar  longitude  and  lati 
tude.  Mr.  Howlett  shows  how  this  may  be  done  by 
three  observations  of  the  sun  made  at  any  fixed 
hour  on  successive  days.  Perhaps  the  following 
method  will  serve  the  purpose  of  the  general  ob 
server  sufficiently  well : — 


106        HALF-HOURS   WITH    THE    SUN    AND   MOON. 


The  hour  at  which  the  sun  crosses  the  meridiar. 
must  be  taken  for  the  special  observation  now  to  be 
described.  This  hour  can  always  be  learnt  from 
'  Dietrichsen's  Almanac' ;  but  noon,  civil  time,  is  near 
enough  for  practical  purposes.  Now  it  is  necessary 
first  to  know  the  position  of  the  ecliptic  with  refer 
ence  to  the  celestial  equator.  Of  course,  at  noon  a 
horizontal  line  across  the  sun's  disc  is  parallel  to 
the  equator,  but  the  position  of  that  diameter  of  the 
sun  which  coincides  with  the  ecliptic  is  not  con 
stant  :  at  the  summer  and  winter  solstices  this  dia 
meter  coincides  with  the  other,  or  is  horizontal  at 
noon ;  at  the  spring  equinox  the  sun  (which  travels 
on  the  ecliptic)  is  passing  towards  the  north  of  the 
equator,  crossing  that  curve  at  an  angle  of  23J°,  so 
that  the  ecliptic  coincides  with  that  diameter  of  the 
sun  which  cuts  the  horizontal  one  at  an  angle  of 
23^°  and  has  its  left  end  above  the  horizontal  dia 
meter;  and  at  the  autumn  equinox  the  sun  is  de 
scending  and  the  same  description  applies,  only 
that  the  diameter  (inclined  23^°  to  the  horizon) 
which  has  its  right  end  uppermost,  now  represents 
the  ecliptic.  For  intermediate  dates,  use  the  follow 
ing  little  table : — 


e* 

>o      «e  |o      I-H 

-*       10  05      o  ,10       in 

Date. 

c<< 

h    <»\ 

w 

(Circiter.} 

1 

1  1 

9  1 
^  s 

$    II    1 

£LI       S   CH       "*5 

1  1 

3 

m 

Inclination  of 

Left 

Left 

Left 

Left      Left 

Left     1,0ft 

Ecliptical  Diameter 
of  Sun  to  the 
Horizon.* 

0°0' 
Right 

6°  24'  12°  14' 
Right   Right 

17°   3'  20°  36' 
Right  !  Right 

22°  44' 
Right 

23°  27' 
Right 

Date. 

S 

t-     *~ 

IN  n 
<N  cq 

*•    <°;8    3 

=0        *- 

CO 

(Circiter.) 

1 

0          ^ 

*  g 

>  t» 

&  s 

£   2'ts   $ 

X    <  o    <! 

2  I 

"ft 

2 

*  The  words  "Left"  and  "Right"  indicate  which  end  of  the  sun's 
ecliptical  diameter  is  uppermost  at  the  dates  in  upper  or  lower  row  re 
spectively. 


HALF-HOURS   WITH   THE    SUN    AND    MOON.         107 


Now  if  our  observer  describe  a  circle,  and  draw 
a  diameter  inclined  according  to  above  table,  tbis 
diameter  would  represent  the  sun's  equator  if  tbe 
axis  of  the  sun  were  square  to  the  ecliptic-plane. 
But  this  axis  is  slightly  inclined,  the  effect  of  which 
is,  that  on  or  about  June  10  the  sun  is  situated  as 
shown  in  fig.  14  with  respect  to  the  ecliptic  a  6  ;  on  or 


Fig.  13. 


Fig.  14. 


Fig.  15. 


about  September  11  he  is  situated  as  shown  in  fig.  13  ; 
on  or  about  December  11  as  shown  in  fig.  12  ;  and  on 
or  about  March  10  as  shown  in  fig.  15.  The  inclina 
tion  of  his  equator  to  the  ecliptic  being  so  small,  the 
student  can  find  little  difficulty  in  determining  with 
sufficient  approximation  the  relation  of  the  san's 


108    HALF-HOURS  WITH  THE  SUN  AND  MOON. 

polar  axis  to  the  ecliptic  on  intermediate  days,  since 
the  equator  is  never  more  inclined  than  in  figs.  12 
and  14,  never  more  opened  out  than  in  figs.  13  and 
15.  Having  then  drawn  a  line  to  represent  the 
Bun's  ecliptical  diameter  inclined  to  the  horizontal 
diameter  as  above  described,  and  having  (with  this 
line  to  correspond  to  a  b  in  figs.  12 — 15)  drawn  in 
the  sun's  equator  suitably  inclined  and  opened  out, 
he  has  the  sun's  actual  presentation  (at  noon)  as 
seen  with  an  erecting  eye-piece.  Holding  his  pic 
ture  upside  down,  he  has  the  sun's  presentation  as 
seen  with  an  astronomical  eye-piece — and,  finally, 
looking  at  his  picture  from  behind  (without  invert 
ing  it),  he  has  the  presentation  seen  when  the 
sun  is  projected  on  the  screen.  Hence,  if  he  make 
a  copy  of  this  last  view  of  his  diagram  upon  the 
centre  of  his  screen,  and  using  a  low  power,  bring 
the  whole  of  the  sun's  image  to  coincide  with  the 
circle  thus  drawn  (to  a  suitable  scale)  on  the  screen, 
he  will  at  once  see  what  is  the  true  position  of  the 
different  sun-spots.  After  a  little  practice  the  con 
struction  of  a  suitably  sized  and  marked  circle  on  the 
screen  will  not  occupy  more  than  a  minute  or  two. 

It  must  be  noticed  that  the  sun's  apparent  dia 
meter  is  not  always  the  same.  He  is  nearer  to  us 
in  winter  than  in  summer,  and,  of  course,  his  ap 
parent  diameter  is  greater  at  the  former  than  at  the 
latter  season.  The  variation  of  the  apparent  dia 
meter  corresponds  (inversely)  to  the  variation  of 
distance.  As  the  sun's  greatest  distance  from  the 
earth  is  93,000,000  miles  (pretty  nearly)  and  his 
least  90,000,000,  his  greatest,  mean,  and  least  ap 
parent  diameters  are  as  93,  91 J,  and  90  respectively ; 
that  is,  as  62,  61,  and  60  respectively. 

Mr.  Hewlett  considers  that  with  a  good  3-inch 
telescope,  applied  in  the  manner  we  have  described, 
all  the  solar  features  may  be  seen,  except  the  sepa- 


HALF-HOUKS  WITH  THE  SUN  AND  MOON.    109 

rate  granules  disclosed  by  first-class  instruments  in 
the  hands  of  such  observers  as  Dawes,  Huggins,  or 
Secchi.  Faculse  may,  of  course,  be  well  seen.  They 
are  to  be  looked  for  near  spots  which  lie  close  to 
the  sun's  limb. 

When  the  sun's  general  surface  is  carefully  scru 
tinised,  it  is  found  to  present  a  mottled  appearance. 
This  is  a  somewhat  delicate  feature.  It  results, 
undoubtedly,  from  the  combined  eifect  of  the  gra 
nules  separately  seen  in  powerful  instruments.  Sir 
John  Herschel  has  stated  that  he  cannot  recognise 
the  marbled  appearance  of  the  sun  with  an  achro 
matic.  Mr.  Webb,  however,  has  seen  this  appear 
ance  with  such  a  telescope,  of  moderate  power, 
used  with  direct  vision;  and  certainly  I  can  corro 
borate  Mr.  Hewlett  in  the  statement  that  this  ap 
pearance  may  be  most  distinctly  seen  when  the 
image  of  the  sun  is  received  within  a  well-darkened 
room. 

My  space  will  not  permit  me  to  enter  here  upon 
the  discussion  of  any  of  those  interesting  specula 
tions  which  have  been  broached  concerning  solar 
phenomena.  We  may  hope  that  the  great  eclipse 
of  August,  1868,  which  promises  to  be  the  most 
favourable  (for  effective  observation)  that  has  ever 
taken  place,  will  afford  astronomers  the  oppor 
tunity  of  resolving  some  important  questions.  It 
seems  as  if  we  were  on  the  verge  of  great  dis 
coveries, — and  certainly,  if  persevering  and  well- 
directed  labour  would  seem  in  any  case  to  render 
such  discoveries  due  as  man's  just  reward,  we  may 
well  say  that  he  deserves  shortly  to  reap  a  harvest 
of  exact  knowledge  respecting  solar  phenomena. 


THE    END. 


LONDON: 

.'RINTKD    UV    W.   CLOWES   AND   SONS,   DUKE  STUEET,   STAMFORD  STREKT, 
AND   CHARING   CROSS. 


U.C.BERKELEY  LIBRARIES 


CD4E57fiSDD 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 

AN  INITIAL  FINE~OF  25  CENTS 

WILL  BE  ASSESSED   FOR   FAILURE  TO   RETURN 
TWB   BOOK  ON   THE  DATE  DUE.   THE   PENALTY 

W"LL  INCREASE  TO  so  CENTS  ON  THE  FOURTH 

DAY    AN D    TO     »1.OO    ON     THE    SEVENTH     DAY 
OVERDUE. 


A  CLASSI 


"  We  know  t 
library."— 2V.  Y. 

"  For  referene< 
"  Supplies  a  m 

"  The  arranger 
may  be  saved,  a 
suiting  it."— Am 


w 


HAT 

givin 
134  Pages. 


"Compact,  sugg 

|;  It  can  hardly  fi 
wits'  end  to  know 


LD  21-100m-7,'33 


Vil. 

HOW  TO  EDUCATE  YOURSELF.     A  complete  Guide 
for  Students,  showing  how  to  study,  what  to  study,  and 
how  and    what  to    read.     It    is,  in   short,  a    "  Pocket    School 
master."       By    Geo.    Gary   Eggleston     (Editor    Hearth    and 
Home}.     I2tno,   151  pages,  cloth,  75  cents. 

"  We  write  with  unqualified  enthusiasm  about  this  book,  which  is  ontellably  good 
and  lor  -jood.''— N.  Y.  Erenimj  .Mail. 
"We  cordially  commend  this  work."— N.  Y.  School  Journal. 

VIII. 

SOCIAL    ECONOMY.       By    Prof.   E.  Thorold    Rogers 
(Tooke    Professor   of  Economic   Science,    Oxford,  Eng 
land),  Editor  of  "Smith's  Wealth  of  Na^  Revised  and 
edited  for  American  Readers. 

This  little  volume  gives  in  the  compass  of  r         /  oncise  yet  compre 
hensive  answers  t  >  the  most  important   quex         /  il   Economy.     ' 
book,    from  its  simplicity  and  the  excelle'      /  action,  is  especially 
9'lantecl  for  use  in  schools,   while  the  inf  ins  is  of  value  and 


interest  to  all  classes  of  readers.     I2ino, 

"  We  cannot  too  highly  recommend  this  w^ 
public."  —  At/terican  Athenaeum. 


H 


INTS  ON  DRESS 


OTTTT.INR  nT«ToiiT  op 
THINGS  INDISVEN^X 
ESTIMATES  OP  CV 


256331 


75  cents. 

'  leut8  ^ 


oman. 


.STB. 

N  IIY  DBKSSIXO  WILL. 
SCITABU.ITY. 


-nse  as  could  well  be  crowded  into  Its 


__  IT   SHOULD    BE,   AND  WHAT  TO 

PUT  IN  IT.  Containing  hints  for  the  selection  of  a 
Home,  its  Furniture  and  internal  arrangements,  with  carefully 
prepared  price  lists  of  nearly  everything  needed  by  a  house 
keeper,  and  numerous  valuable  suggestions  for  saving  money 
and  saining  comfort.  By  FRANK  R.  STOCKTON  (of  Scribner's 
Montniy}.  izmo,  182  pa"ges,  cloth,  75  cents. 

"  Yonng  housekeepers  will  be  especially  benefited,  and  all  housekeepers  may  learn 
much  from  this  book." — Albany  Journal. 

XL 

THE   MOTHER'S  WORK  WITH  SICK  CHILDREN. 
By  Prof.  J.   B.  FONSSAGRIVES,    M.D      Translated    and 
edited  by  F.  P.  Foster,  M  D.     A  volume  full  of  the  most  prac 
tical  advice  and  suggestions  for  Mothers   and  Nurses.      i2ino, 
244  pages,  cloth,  $1.25. 

"  A  volume  which  should  be  in  the  hands  of  every  mother  in  the  land.1'—  Binghamp- 
ton  Herald. 


mimim 


